Moving the barrel further back will increase the gap at the front even more, I think it may cause air seal and feeding issues. And yea, as you said it would be "pita" to align everything correctly...
I've compared MR HOP and DECEPTICON buckings by dropping bb into chamber at zero hop and noticed that with decepticon bb stops at the start of the bucking patch while with the mrhop bb stops at the middle/end of the patch, still did not have a chance to test the differences in the field.