I feel your pain... but in the opposite foot.
I'll just offer up what I've settled on this season as it's quite different than anything I had previously ever done (and I've never seen this suggested by anyone else). This might work for you too. This technique gets my feet situated best in the heel/ankle pockets without needing to bang my boots on the floor.
After slipping into the shells, I close the power strap first. While standing, I pull up on the rear loop of the liner while flexing forward in the boots (no buckles closed). I do this repeatedly until my heel is fully back. This works best for my liners/shells to get my foot seated into the rear of the shell.
With my feet situated, I buckle from the top-most buckle on down. Keeping the buckles fairly loose until I'm at the top of the first lift. The key buckle for "performance" is the ankle buckle (second down). That's the only one I buckle more tightly, but this is AFTER I got the instep area to fit correctly (with no gap/slop over my foot).
I'd recommend this method pretty much...
I just use the top buckle first (rather than the powerstrap) - it's not levered closed, but close enough so a good flex forward gets your heel back into its pocket (and your toes off the ends of the shell) without alarming the owners of any expensive carpets or wood flooring by doing the heel bang alternative.
NOTE:- your boot doc liners are lace up like my Zipfits... so i'd imagine from the positive reviews i've seen of those boot doc foamed liners, that once snugly laced up your heel/ankle (and foot) is already nicely and firmly held in place, no slop or heel lift etc.
Thanks to this you do
NOT need to do those two top buckles up very tightly at all - they will and can and should be far less tight than the 'regular' liner.
A normal liner you're having to crush the shell closed to get the liner tightened around your leg and foot - wiht your Boot docs (or zipfits) your foot is already secure in the liner, all you need is the liner to engage and be close
enough to the liner, and oncer your heel is in the pocket there's even more security.
I have the forefoot buckles only done up enough to stop them rattling, like most i'd guess.
The difference is the top two buckles.
Before you're probably used to having to use the heel of your hand to get enough leverage to close those buckles tight enough.
Stop! Don't!
With my Zipfits, I only need the kind of buckle tightness that can be closed with one finger (!) - so for sure give it a go as that will keep your circulation going for warmer feet and comfort but still with control and heel hold. (I suspect that with your previous liners needing the boot to be buckled up especially tight on your 'bad' foot that you're still cranking them down far too tight).
Hope it helps... and it's an easy thing to try - don't be alarmed by how 'untight' those upper buckles seem compared to before.