There is indeed some form of 'logic' in the default chosen account. With iDEAL / SOFORT payments this will always be the account at the top of your account overview, by changing the order it will change. For SEPA transfers and Requests, your last used account will be used for that type of payment.
Personally I would find it easier if it is always the top account and so there is no distinction between the type of payment, so you always know that you have to check this. Or an explicit screen in which you have to choose the 'from' account.