The majority of older motors (before everyone jumped on the short stack bandwagon) were track tested to find an optimal setting, then measured on an analyser to check the current draw. In general they drew in the ballpark of 6A. It was a pretty good rule of thumb back then, but with the shorter stack motors it's not always (but sometimes is) a good starting point. I think the Team Scream motors from a year or 2 ago were particularly sensitive, I've seen reports of them performing far better at the 3-4A range.