Span21 has been my preferred game for a couple of years now.
However, the rules, no. of decks, and penetration, differs depending on where you are playing.
On several occasions I have had floor persons suggest to players that they go to wizardofodds.com
for the correct basic strategy; as well as settle arguments among players with the correct B.S. play.
Incidentally, getting heat at the game is not as rare as it once was. I have been backed-off several times
even though my stakes were low and spread was moderate.
What geographic area are you referring to ?