i found, if you crank it all the way tight like that, yeah, there is lots of squeeze. but also found that if i gave it just a little sag, you still lay straight down the middle relativly flat, but i experienced about the least shoulder squeeze possible. i can experience the same thing when using lots of sag, laying straight down the middle produces near zero squeeze, but since you are hanging with lots of sag, it may be uncomfortable to lay that way for other reasons, like banana curve or more knee hyperextension or whatever. so it works better when you have little sag and laying down the middle would be relativly flat on its own.
i've been using a clove hitch with the 3mm vectrus 12 as well lately. well, at least a couple times. i was able to get them to break relatively easy also. just by pulling the lines in the right directions, i won't try to explain.
i'm sure you are aware, but watch those tree strap loops, that line is moving through there when you tighten, and when you tighten it tight there is some force as well. i've been hanging from 4g welded steel rings lately to avoid wear on the tree strap loops.
it is a sharp looking suspension setup you got there by the way. the blue doesn't look too bad, why didn't you get the grey, looked like aps had amsteel blue in black or grey one.