It is working!
The irritating thing is that I never got to retry backstabbing with the axe
before uninstalling Sims tweakpack components of improved backstabbing and additional racial enemy components (the latter of which I weren't using anyway, so that was mainly because I was lazy, and there was a rumour about that one about)
For what it is worth, right now, at least we are down to one of two possibilities:
either, I was somehow doing it 'wrong', OR the improved backstabbing/additional racial enemy components from Sims tweakpack version 14 has some kind of influence, anyways.
But this time, I'm actually suspicious of how I carried out the experiment the last time...
If my F/T simply never experimented backstabbing with axes versus shortswords on any other than the tougher Duegar warriors from the Tactics mod (the most plentiful opponent in chateu Irenicus when using the improved Ilyich) and therefore simply never managed a hit in time for his backstab to work, that might have erroniously convinced my untrained eye (used no backstabbers playing through BG1) that I simply weren't being allowed to do it... The fact that the shortsword backstabs where an instant success could be attributed to simple coincidence.
My selfsuspicion is made quite plausible by the fact that now, the backstab works every time on the 'imp ilyich' mages, but only rarely on the warriors...
much ado about nothing, I'm affraid.
Well, at least I
now know it
is working.