I don't make that many payments myself, but the flow has changed a bit (on Android) since I last used it.
Pretty much always I pay with pin or iDeal and the account selection is the first step. A new payment request starts indeed with only an amount and nothing more. The source account is only visible on the summery screen.
The the account selection is the first step, than the account with it's balance can be shown when you enter the amount you wish the transfer..