I've always had issues getting a proper fit and seal with the Alpha Dog (2 tour demos, now my personal pair), which contributes to channel differences, most noticeable in how the left channel is presented and differs. There's a good chance your situation is like mine and that it entirely comes down to fit and seal.
After some adjustment, they fit and seal without too many issues now. But they are still on the picky, difficult side compared to most headphones (will probably get better as I continuously adjust them). Here are some tips:
1. Give the pads a couple days to fully regain their shape after being shipped.
2. Give them ~10 mins on your head to warm up before really worrying about super proper fit/seal.
3. Try adjusting the rotation angle of the pads and varying headband positions on your head. Experiment with varying height settings (might need to be a bit looser or tighter than you expect).
4. Try adjusting the shape of the original Fostex headband. I had to bring mine more to a point in the middle, for example, as it was a bit too flat/square otherwise and cause the cups to not fit/seal as well as they should. This made the biggest difference for me.
If, after a lot of experimentation, you have no luck with this, might be best to get it checked out.