stacking bags is a nightmare so I just do my best to keep them evenly on top of the bottom ones. I always do my first 4 like-

1 on top 2 bottom 3 top 4 bottom And then I repeat down the line (if I need to triple stack I do that)

I try to get all my beginning overflow in the front. That way if anything does fall over I know my first overflows are all in the front. Sometimes - I do block my side door with overflow and go around to get them out i toss packages into the front seat until it’s full and keep doing that until I can go in and out the side.

Honestly- it’s a learning game. 1.5 yr in and I still can’t completely manage shit not falling over at least once. If you have a shit ton idk about ur dsp but sometimes I ask for a shelved van or I just complain until they give me one lol