I'm not exactly sure what this means. When I pay $20 cash for a deposit in a bitcoin account what is the exchange rate? Do they use the MtGox spot price at the time of the transfer? I'm not sure since it says you will receive $19.22 in the account after fees but we all know BTC accounts are not denominated in USD.
I could be mistaken but I think theyd use the mtgox price at the time of transfer. $19.22 worth of btc in your case. Theres a stickied support thread at the top of this section, might be better off asking there.