I just don't see how I can get the frame under the backplate. It just does not fit. It's out by 2-3" at the top. I keep lowering it still won't fit on.I just went through the same struggles with my jetpack. I have lots of youtube videos on my build starting here
I just had to keep lowering it till i got it where I wanted. Also had to move the hardware on the jetpack itself. You will get it!
You may have to move the hardware on the jet pack higher so that it catches in a different place thus allowing it to sit lower. Do you know what I mean ? I couldn’t move the bar on my harness anymore so I raised the metal clips on the jet pack about 3 inches higher so that the jet pack could fall 3 inches lower . Does that make sense ?