All fair BTC slot machine games have one thing in common: the outcome of each round is based solely on a random number provided by a Random Number Generator (RNG). The random number generated by the RNG "tells" the reels when to stop and therefore decides the game's outcome. This means that the same game with the same random number should always give the same result.
The higher the value of your bets, the higher (usually) the rate of return to the player from the betting system. Assuming all other rules of that system remain the same.
1- The RNG generates a random number.
2- The game's math module gets the random number and calculates where the reels should stop.
3- The game stops the reels at the given positions and calculates the result of the round.
4- The result of the spin is then displayed.
Your win (or loss) on each spin is determined purely by your luck. The result is not influenced by your previous win/loss, nor the win/loss of other players, nor anything predictable.
Modern RNGs used in online casinos are dedicated hardware devices that generate random numbers from electromagnetic noise. The hardware RNG generates thousands of random numbers every second. So, on the one hand, you change the outcome of the next round if you press the "start" button a second later. On the other hand, you have no chance to predict whether the result will be better for you or not. Therefore, fair randomness remains.