lol sorry i wasn't more helpful in that regard.
the rc, they do put more pressure obviously than the front, but it will depend on the size of your ass and torso structure in general how much pressure they put. what does your routine look like, as in when on what day of your split do you do the shrugs?
the other exercises i was listing were just alternatives that i use to target that same area, the single arm curl was meant to be single arm shrug, and i can give form advice on those if you're not familiar. the single arm is nice because you can position yourself a few different ways to hit your whole traps.
an alternative shrug exercise you might not be doing that can target mid-upper or mid-lower well depending on how you do it is overhead shrugs.
anyway, my bad, reading the first part of your post it seemed more like you were opening up discussion about it more than asking for specific advice... i then apparently went totally ray charles on the last line 'cause you were more than clear there.