Sheaf advice

I am tossing a 20lb bag this weekend for the first time.  With the 16lb bag, I start 4 paces out from under the bar.  Does anyone come in closer for the heavy bag, or toss from the same spot?  Any tips?

Same. 4 1/2 steps out. Make sure you come in at a lower height.

Newb to the sport so take it as such...

Throw from the same spot but be very attentive of your technique or have a buddy watch you. In regards to those who throw with their backs to the bar. Quite a few guys I've noticed (me included) tend to mistakenly slip in one or two bad habits when putting in more effort or throwing the heavier bag - that is torquing around (rotating the hips/shoulders toward the bar and/or looking up) to watch the sheaf go over the bar, which will tend to cause over rotation as well. Both can misdirect the power put into the sheaf and effect its flight path as well as diminish the effectiveness of the block.

but I may be full of it...

EDIT: see you've thrown 34 feet Nathan, nice! Eventually I'll know who you guys are by name - *facepalm*