I have concerns too about computation of RTP, I stumble on evolution gaming games like monopoly and crazy time, they are not actually slot but they still have RTP, I wonder how they come up to there declared value while the game has different betting option.
These games also have a house edge, so theoretically, RTP is 100% - HE.
There are different option on slot that you can add more lines to bet so that you increase chance of winning. Is RTP percentage will be the same?
No, more lines = more RTP (generally). For example, in games like Hotline, Book of Shadows, adding more lines will change your winning probability, thus change the RTP.
AFAIK, RTP is the return to player over time so if I have a hundred bet, 90% of my bet will be my profit if the RTP was 90%.
There are two kinds of RTP, (1) theoretical and (2) actual/live.
(1) Theoretical RTP is basically what is being programmed, which will/should be accurate after hundreds of millions of spins. Let's say the total input was $100,000,000 the software should produce the output of $90,000,000 (assumed 90% RTP).
(2) If you only do hundreds of spins, you still play on a 90% RTP software, but the actual RTP will be based on your luck. If you walk out smiling with a double bankroll, then the live RTP is 200%.
For more info visit:
https://bitcointalksearch.org/topic/slots-103-more-in-depth-about-return-to-player-rtp-with-poll-5268333