Good Morning gfm,
One solution is what Hossein Karimi mentioned; to create separate account structures for example for your P&L accounts and for your BS accounts.
That is, if you include your bank accounts in an account structure for the BS (balance sheet) accounts that only contains the main account dimension.
All of your expense accounts are included in the P&L account structure that include BU, Dept and CC.
Then things work as you want.
If you shun making this setup try the following:
Enter your bank account on the left hand side of the journal in the account section and enter the ledger account on the right hand side.
That is, simply 'flip' the posting.
Doing this will shift the findims setup for the bank account to your expense account.
As your bank account has no findims configured you can also reach what you are looking for.
Best regards,
Ludwig