Lower the SCBA and tighten the waist harness. The shoulder straps should not dig in, as the waist should take the bulk of your weight to protect your back.
Lower it and see how it feels. I went through the same thing when I first started wearing one. I tighten the waist strap around my hips, it's a good back support as well! :)
We did that - we switched to the "Stealth" cylinders for our MSA Firehawks. They ride lower in the pack frame than the standard SCBA cylinders and the helmet-cylinider banging problem instantly went away.
Here is an answer that I didn't see on here. How about a longer neck on your body. Just kidding I had the same problem one I am considered a no neck. I only stand about 5' 7" so it gets a little rough at times. But the good news is now I am a traffic officer with the Emergency Management when I turn up my coat collar in the winter time it actually does some good.
I used to have that problem with our old packs.I wear a Houston and it was a pain in the a**.We got new packs last year and it was a major difference.They are designed to ride lower on your back.Much more comfortable than the old ones too.
Take that problem into consideration when you are purchasing replacement SCBA's We recently purchased new ones with a FEMA Grant and went with the Scott 4500 psi 30min composite cylinders and it's a world of difference!