what you land on is the coin bonus the game gives you for buying coins. so if you land on a 2x spot you'd get what you bought in coins in game. so i buy 500 ap worth of coins after landing on the 2x space. it would pay me out the max it would give you. 1.5k free coins. so you'd technically get 1.5k coins at the most regardless of topup. but this way is the most ap efficient.
long story short it paysout free coins based on what you land on in wheel. paying NO MORE than 1.5k coins in mail.