your problem is wide FH due to your knees. Given the state of your knees and the quality of your BH, i think it would make sense to position yourself a little bit more to the center of the table to cover better your FH side. sometimes you would have to make a little step to take those deep BH balls, but i think thats ok PLUS given its your strong side, you would be able to compensate/adjust easily if you can't move.
On the other hand, being in a better position on the FH side means this side won't be such a weakness anymore. actually could be much better, you already have FH power. you will be able to take those wide balls earlier, make better blocks etc...
----
as for me, i was directed to do that as well for opposite reasons. I was a FH player and relying too much on my FH. It meant pivoting a lot, but i was getting slower at it with age, PLUS exposing my wide FH when pivoting. By changing my position a bit, it forces me to play MORE BH. and my FH side is even stronger. I pivot much less than before. My BH has gotten much better during rallies but 3rd ball attack / attacking vs backspin with BH I'm not consistent yet. My percentage can change too much on a different day or different player.
Of course, in a match, if i feel I'm not in a good day with my BH, i'll go back to playing more FH and anyway during the match i will always try to pivot at least a few times just to confuse / scare the opponent, even if i miss. but its not the main tactic anymore.