Super Times Pay poker question

A great advantage video poker players have over slot players is that we can figure out the house edge by looking at the paytable. But the Super Times Pay game (and a several other similar ones) have a random multiplier which pops up now and then and increases the payout for hands. How can we figure the effect of this multiplier on our overall payback? Can't the casino tighten and loosen the frequency of appearance and distribution of the multiplier amounts at will, thus putting us into exactly the same boat as the slot player?

Check the Wizard of Odds video poker page. He says it adds about .27% to the overall return.

Thanks for the lead - I had not seen that the probabilities of the multipliers are spelled out in the rules of the game. It's nice to know the sixth coin is a good bet, although it certainly does increase the volatility!