Does the height matters for player?

[Toxcatl]

1) Height matters for heading, I bet. For some goalkeeper actions as well, probably.
2) Correct me if I'm wrong, SA works only on those positions it could work. You can't train Playmaker to a pure defender, therefore, it won't work if the player is on D* position. I'm not sure, to be honest.
3) Sounds highly implausible. There're many factors that affect players performance, I don't think this one have any direct influence.