As I funderstand it, if I keep my FB 'IN', then his attributes are 'rolled' in with the OL? If that is the case, and my starting five OL average 90 in their STR rating and my FB's STR rating is a 75, am I best to not keep him 'IN' as his STR rating would bring down the OL average?

Or, does having the FB as a sixth blocker have some other impact/effect that I am not considering?

This question could also apply to TEs, I guess.

This is a fantastic question and something I have also wondered about. Also applies to LBs on the line. The problem is no one will have an answer. Only theories.

I'm not sure of the actual mechanics involved, but I believe that WIS said in a dev chat that adding an additional blocker(FB or TE) always positively effects your ability to block on that play regardless of that players ability.

Better blockers are going to have more of an effect of course but the additional body in a spot always provides some help.

I'd assume the same thing applies to LBs playing line but I'm not certain on that - again the actual mechanics are a grey area.

you will notice that the FB is described, if his job is to block, as in/out

you will notice that the FB is not ascribed, in position roles default if i rem right, speed

so my conclusion is he is always johnny-on-the-spot at the point of attack

as if by magic a +1 die roll modifier

if you use a 75 str fb to block up the middle he probably isn't going to perform great for you. strength is the most important attribute for blocking up the middle. on the outside, strength doesn't matter nearly as much. blocking is key outside, ath, gi, tec to help.