What one session can and cannot tell you
Symbols land at random across the 5x3 reels, and Scatter symbols start the bonus round. How often that happens is not known before play. The result of one session is random as well, and the RTP does not change that. RTP describes the return over a very long run of rounds, not the outcome of your next visit.
Each spin on the reels runs on one RTP version, and that version is shown only in the game rules. Check the game rules to see which version Imperial Casino runs before you compare returns between sessions.
A winning combination on the reels can pay up to the maximum win of Big Bass Splash 1000, which is a ceiling and not a typical result. That ceiling is reached very rarely. The maximum multiple stays the same at every bet, so the money figure grows with the stake.