Bruzer,

It's a common misconception that one end or the other of a scope controls parallax, but as you noted it's essentially the entire system.

With many lower-powered scopes I've found small amounts of parallax at 50 yards can be adjusted out just by focusing the rear end, but it doesn't work with all scopes.

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck