Your problem is that you have one pair of normal boots and one pair of reduced footprint boots. The fact that you couldn't get your Salomons to even center in the medium bindings baffles me to no end. My only though is that you didn't know how to use the adjustments and the mounting disk to center the boot correctly. Not trying to offend but it is all I can come up with.
I would love to see pics of your K2 boots in the large bindings to see what they look like.
No offense taken, I'm pretty sure there was no other way to do it, but I'm open to the possibility that I overlooked something.
The thing is though, the centering on the board wasn't the only problem. The footbed was fully extended (which doesn't actually go out much further) and when riding on them, I had over 1.5" of overhang on the supposed "reduced footprint" boots. I could actually feel the corner of the foot bed digging in to my boot under the metatarsal area during a toe-side turn. There is no heel cup depth adjustment on these (that I can see), so it wasn't possible to put my boots back any further.
The centering issue on the Medium is sounding like a correctable issue. I know that we could troubleshoot that one. We fit the overlap sizes to your boot size every day. Was the disk adjustment all the way back for the 7.5 (hardware in the most toeside holes)?
Yes. If you haven't looked recently, I'd suggest taking a look at how much space that really buys you on the flow plates. It's less than half an inch. After doing this, my toe overhang was about 1.5", and the heel of my boot was still about a quarter inch *inside* the edge of the board. As in, not even overhanging yet.
As requested, pics of the T1 boot in the Large.
Photo Album - Imgur
Pic 1: The Salomon 7.5 on the left is not much smaller footprint-wise than the K2 8 on the right. The toe area is a bit more bulky, enough that the Medium flow binding cannot go over it even using the last tooth on the ladder and the other side of the strap extended all the way to the plastic guard edges holding it in.
Pic 2: Binding centering. This pic is using the burton channel holes, and as you can see, there is very little room to center the binding left or right. Less than half an inch. On the Large, it is currently centered pretty well and I have it all the way towards the rear. When I had the Mediums, it was actually mounted on a Lib board with traditional 4x4 mounts. In that case, the base plate is rotated from what you see in this pic, and you can slide it left or right along the 4x4 holes to center. On the medium binding on the lib board, I had it rotated and all the way to the right (rear), which brings it closer to center by about 0.5" or less. You can see based on the scratched paint in this pic that the center of the holes were used (because this is a pic of the large, which centers nicely enough using the center holes). On the Mediums, you would have seen that wear all the way to the bottom.
Pic 3: My older, size 8 K2 boots in the Large flow, similar to my previous pics. Note that the upper binding strap is all the way down (visible in next pics), in attempt to center the pressure at the instep area and uniformly around the boot. The green strap is as small as it will go, and as was the case with the Salomon boots, it just curls way up and may as well not exist.
Pic 4: This is how much heel lift occurs with centering the upper strap and flexing toe-side. Not a whole lot, and it is possible to ride like that. I could probably live with that much heel lift if there were no other issues. In fact I would guess it is comparable to other bindings, haven't really checked.
Pic 5 and 6: After lowering the highback and pulling my foot out after the initial setting, then reinserting as best as I could, much better than I could if my other foot was in and I was on snow, I re-did the same action from Pic 4. As you can see, there is more heel lift. Not nearly as bad as the Salomons, but not very good. After closing it upon reinsertion, I did observe the toe cap being more prone to sliding than my initial settings.
Pic 7: This is an attempt at "best fit" rather than even pressure. The problematic green strap fits over the middle of the foot nicely. The right side of the upper strap (not visible, but visible in the next pic) is not shoved so far down the strap that it's interfering with the cable. Although this setup looks like it fits reasonably and clean in all areas, there is far more pressure on the left side of my foot here, and plenty of soft on the right side to roll my ankle. The real issue is evident in the next pic.
Pic 8: Note that the strap is further out as mentioned above. This is with the ankle ratchet as tight as it will go, flexing toe side. Tons of heel lift.
Pic 9: This is roughly what the Salomon 7.5 boots looked like with overhang on the Flow size Medium binding. It's just an approximation and I'm actually showing the Large binding because I already returned the Medium. I rode on the Mediums like this, and aside from the centering issue mentioned above, the amount of toe overhang was really awkward and I could feel that corner through my boot when applying a lot of pressure for toe side turns/carves. The angle here looks like 2 inches but it was more like 1.5".
Pic 10: For comparison, this is the same boot in a Size Medium K2 Sonic binding, with the footbed/gas pedal fully extended. Fits more or less perfectly, flush with the boot and negligible toe overhang - mostly just boot material.
To clarify, I don't care about fitting the K2 boots to the flows. They're my old pair and basically retired. My goal is to use the Salomons. I just wanted to demonstrate that even with those at size 8, it's a really poor fit for both the M and the L. However, if you see anything here that might make the Salomons fit *either* binding, or any adjustments I missed, I'm all ears. I'd have to return and exchange again, which they said I can't do after I ride on them, but I'll put up a fight if you think that the Mediums are workable despite the issues I highlighted.
If you have any Medium NXT flows in stock, I'd encourage you to grab a 7.5 or 8 boot and test it in there and take a look at the overhang. Given that I found it was huge with 2 different boots, I suspect your experience wouldn't be any different. I appreciate your help though, and although I already bought these from Evo (and your website suggests you are out of Mediums anyway, on the off chance that there is a way to make those work), I'll make a point of purchasing from you in the future