You talk about 'F' for Crouch(cover) and the middle mouse for Taking cover(or rolling into cover, or putting up portable cover) when in fact the F key will do both. In the early stages of Beta there was a difference between the two, now it seems that they are on in the same.
1.If you have no target 'F' will put up PC.
2.If you have a target and there is no gumby 'F' will put up PC
3.If you have a target and there is a gumby 'F' will roll you into the gumby.
With rolling into a gumby bugging out Aimed Shot I just run to the cover spot and use Shift+F.
Great write up by the way.