Though if you look at the NoLimit City report system (not the one on the slot screen after the bonus win) buy feature winnings multiplier is calculated by winnings /cost of buy feature.
NoLimit City doesn't report it by winnings / cost of buy feature. It's winning / bet amount. Proof below, you can look at my buys on this slot, these are at .10c bet amounts
Here's the replay of my 425x
https://replay.nolimitcity.com/show/kirureoberu?device=desktop&language=en