Lay/Buy Wrong on Craps v2 Game

Buy and Lay bets seem to be calculating wrong on the free play game at https://wizardofodds.com/play/craps/v2/ or I'm really confused which is possible.

Notes say: Lay bets pay true odds, but player must prepay a 5% commission, based on the possible win. This works out to odds of 19-25 on the 6 & 8, 19-31 on the 5 & 9, and 19-41 on the 4 & 10.

Buy 4 for $10 pays $19.50
- logic seems to be charging 5% on the bet amount not the win
- $10 × .05 = .50c

Lay 4 for $40 pays $18.53
- logic seems to be charging 5% on win amount
- but its deducting that from bet amount
- then paying true odds
- then taking another 5%
- ((40-1)/2)×.95 = $18.53

I had $9,959 with $41 on the Lay 4. It won. My finishing balance was $10,019, and my $41 bet was returned to me with $19 in the "won" box.
At a real table, you pay $41, dealer takes the $1 vig, pays you $20 + your $40 bet on a win, or $19 to keep the bet up.