You cannot make any adjustments to prevent the chain from moving over a sprocket on the rear. It will tend to do to find a straighter chain line when the chain is coming from too much angle.

But there's a fundamental difference between the cuts of front and rear sprockets. Cassette design assumes that the chain will be fed straight onto the sprocket by the derailleur pulley, so the teeth are cut fairly square. OTOH, chainrings are designed to accept chains coming from a range of angles and the teeth are beveled to points to help them pick up chains coming from the side. In normal use a chainring should be able to pick up a chain coming from all but the most crossed over combinations without need the FD to guide it. In fact the chain should never be touching the FD cage at all except during a shift.

While it may not be possible to totally avoid the chain coming off when backpedaling, this should be a rare event, except when badly crossed. As I said in the earlier post, if the chain chronically derails when backpedaling it's an indicator the the lower loop chain angle is different than the upper loop's, which usually means a mis-aligned hanger.

I still hold that 99% of the backpedal chain fall-off issues are solvable, and this is a good demonstration of the difference between mechanics and those who hang components on a frame and hope for the best.

To the OP, if you tell us the city you're in, I might be able to refer you to someone who can solve the problem. If you're in the metro NY area, I'll do it for you for free.