Mr. Gypo, that does sound like the only reasonable mechanics, and acceptable source (you) for such i've ever heard for such practice! (see, i don't always have to antagonize the climber-logger stuff!!)
i've also read that coming thru the fibre at a slant on backcut is inferior by the way that the fibre releases instead of coming straight thru (never understood it, jsut read it!).
i kinda found myself sloping backcuts years ago; it does seem safer; kinda like you're not sure, and it seems safer like a large backstop. Even done it on something leaning slightly back from lean (with high, high leverage, braced line for pulling home); until reading contradictions.
Dent is the man! Took me a while to realize that chasing the forces into the face with patterned backcuts was the same patterns as same in bucking, only turned to whatever angle compression and tension of fibre was compared to face, as diagrams in chapters are pages apart. i've taken these lessons into the air, and they still test out wonderfully!! So now every cut places a face at workable position, preloads the opposing fibre specifically to lean with pre-backcuts, then come thru on final backcut seeking fibre in hinge to balance pulls of opposing lean side (or pushes from brushing trees on same side as thicker part of hinge); so that pulls across the face are balanced as hinge folds. Then also, faces slapping is balanced to serve out squarely into gunned face.
Unequal pulls during travel on hinge, or unequal (side to side) pushes at closing face; can quite logically compromise mechanically serving spar forward squarely into path of facecut.
It is all about balanced forces, or as close as you can bring them for safest, most predictable folding, IMLHO.
Just like moving anything else, if it is off balance, you must fight that off balance the whole time of motion, rather than all efforts just pulling spar home on hinge (making hinge stronger). i think that the first part of force calculation is direction, then how much. If direction is not right, it must be fought every inch. Kinda like moving a refrigerator balanced on a cart, or leaning off to one side of 4 wheel cart the whole time you are delivering it. Balanced will be less effort, safer, more productive; for there is magic in balance! You can feel it on a motorcycle, and see it in many things.
:alien: