High temps and fast draws work better than low temps and slow draws, in my opinion. I guess theoretically speaking it would be the same thing but I find it's easier to get it right with a high & fast draw. With the standard setup you should be hearing a wispy, whistling sound. With the ground glass setup I hear more of a whooshing sound.
Also, it may not have anything to do with the unit itself. Since the glass parts are all hand blown there's a slight variation in size of the intake and outtake hole of the HC's. The chamber size of the wands varies slightly as well, particularly in length. I find I like the shorter wands more but they'll be easier to combust with because the load is closer to the heater. Also, the hole that the screen sits on in the wands vary slightly. None of these variations will make or break the unit, it just requires slight adjustments in draw strength.