Thanks to ESPN for introducing me to this game. I first saw it when my family went to a BBQ restaurant for lunch, and the TVs were tuned in to ESPN coverage of the professional leagues for this game.
If you take the distance between the moon and earth, divide by the sine wave frequency of a bean bag flying through the air, further divide by the distance from the earths core to the surface, you get 27 feet, the ideal distance taking gravity and momentum into account. Easy Peasy.
The variation you mention doesn't sound fair or sportsmanlike. It sounds like if the score is something like 20-19 and one team gets to 22 in the next round, they will eventually lose since 13 is so far behind the previous round's scores, so being semi-bad at the end would be encouraged in order to win. I think players should do their best, and if that means one team reaches 21 points or more, so be it.