I suspect that generally people release layouts with a higher % than the arcades. These things can be changed with the config section in the emulator while the game is loaded and in ‘edit’ mode. Depending on the machine rom (game software) both stake and % are changeable but it’s not always the case.
You’ll find even on the higher % the machine will play pretty much as you’d expect in real life as this is emulation rather than simulation. Most UK slots are compensated, so a setting of 70% means that every £10 played yields £7. Though the machine doesn’t have to meet this over £10 worth of plays, I don’t know the exact cycle but I’d say over 1000’s of spins it will be close to percentage.
Also a lot of UK machines would have a separate pot which saved for a big streak, so when the machine was streaking, for example Barcrest Blue Moon would have a very defined streak whereby it would offer nudges and wins every other credit till the streak was over.
J