I have been using an NXS 5.5 to 22 since last summer and haven't noticed the "knob in the back" problem. I'll look for it now that you mention it.
Meanwhile, I just ordered a rifle scabbard-backpack combo from Nimrod Packs at www.nimrodpacks.com.
You can use it without the backpack, too. In this mode it is a scabbard with shoulder harness system that sounds a little like Browning's product but with a scabbard. I tried it out at the Safari Club Convention last winter. Very easy to deploy the rifle quickly. It would be particularily good for carrying a heavier rifle in the 12 pound and up class. I bought it partly in case I need a longer horse scabbard for my 30 inch barrel on my sheep hunt next month.
I love my NXS, by the way. May get a second one soon.