Couple of things may be sabotaging you here. The most common issue is people are not aligned well with the board. Make sure your hips, torso and shoulders are all well aligned with the board and turn your head to look straight down your front shoulder.
Second issue is one you eluded to. Sounds like you are still using a "setup carve" for spinning. Any significant carve on the takeoff will generate rotation. Yes, I said to generally avoid flat basing but, there is a caveat to this. On the takeoff ramp for jumps, I do infact transition form being at low edge angle on the approach to totally flat based just prior to popining off the lip.
I also recommend a two footed pop rather than an Ollie for any jump with a kicker. The pop is a much more stable maneuver than an Ollie and generally allows your takeoff to be more stable.
Wen in the air and going for the grab, pull the board up to you rather than you reaching down for the board. Reaching down will usually start a roll in the air.
In the ATML model, you Approach needs to be stable and that means speed and trajectory so you should not be in a hard arcing curve up the takeoff ramp for any straight air.
This is helpful - thanks. One follow up. Should I be flat basing at the base of the ramp and extending my legs on a flat base all the way to the lip with a flat base pop off both legs?
Do I do a small carve on the ramp to get straight alignment at the top and go flat base just before reaching the "pop off" point at the lip? From your wording above I'm guessing this "last minute flat base" is what you do but I just wanted to clarify.
Thanks as always for your help