I'd pull in your suit again next session.
1) Get your feet set,
2) bend over at the waist,
3) get a vice like grip on the bar,
5) arch your back and HOLD it
6) and THEN wrench yourself down to the bar by bending your knees and get your hips close to the bar.
The start position WILL be uncomfortable. You won't be able to do this with a lighter weight because the weight will fly up when you get into position, THAT is why you typically start with straps down.
Straps up as the weight is heavy enough to keep you down while you get into position. You should be a tight coiled spring at the bottom, then blast off. that will make the most out the gear.
Few additional tips:
1) If your belly is preventing you from getting set properly, lose or loosen the belt.
2) Your upper back is NOT weak, start with the back position you want to finish in.