If you are referring to using the non-channel holes for mounting on a channel board (there are only two channel holes) you should not.
When you have the Medium bindings back please send an updated photo and we will walk you through the best setup steps. In the meantime, Waht is the width of your board at the inserts where you are currently mounted?
No, sorry...disregard the board you see in the pictures. I have two boards. The pictures depict the Large bindings on a different board, which is centered fine. Those pictures were only for demonstrating boot fit problems on the Large.
When I tried to mount the Mediums, I used the 4x4 holes on a Lib Tech board with the normal 4x4 pattern. The 4x4 pattern on a 4x4 board lets you have some wiggle from from center in either direction, as you know. You can slide it in the mount holes in either direction by 3/8".
After sliding it forward in the 4x4 on the 4x4 as much as possible (so, screws all the way to the end on the toe side), I was 3/8" closer to centering it, but with a boot in, there was still huge overhang on the toe side and the heel was not even overhanging yet.
Pics on the actual board:
Note: I am goofy, toes are on the left side.
This shows the 4x4 holes mounted centered:
My boot was way over the edge of the front and not over the back. So I moved these back as much as possible:
That brought me about 3/8" closer to the back, but it wasn't even close to enough. My boots looked like the example on the left here:
I did not know about the heelcup depth adjustment though, which john doe just pointed out. Depending how much room that buys me to get my boot back, it may solve my problem.
Oh, one other thing I noticed. Since you are using a channel board you aren't set in what holes to use. Like you can turn the disk about 45 degrees and use two of the holes for teh 4X4 pattern to bolt down the binding. The degree numbers won't read right but that doesn't matter. Just another way to get more adjustment.
You can't actually do that btw. The 2x2 holes are slightly larger than the 4x4 holes, because the channel holes on the board have to fit through them. They're small cylinders on the board that protrude and stick up through the 2x2 holes, and don't fit through the 4x4 holes (I tried).