There are no real restrictions on online slot games software providers on the first RTP they place on their games. Neither the UK Gambling Commission nor any other government regulatory body has definite legislation that imposes a statutory minimum on online slots games; hence the providers are at liberty to set their RTP however they want it. The paytable and symbols determine the levels of the game. This is why different games have different levels, implying different payouts. These are developed to ensure the slot machines are attractive and unique while giving the casino a house edge. Online slots with the highest payout percentages are the best slots from the players' perspective.