The hi flows put the aperture out further from the center. So the same amount of vertical pellet movement has a greater cross-sectional flow area.
IMO the non-hi-flows should be called flow chokes, cuz when you look at them full open it makes you wonder who the twerp was that thought of doing that, so you could call him up on the phone, and voice your opinion,lol.
And yeah, the stat sets the minimum water temp.If your system overcools, the stat will begin to close and attempt to maintain the coolant temp at or near it's rating. Once the temp is above the stat rating it is supposed to be wide open and doing nothing.
