To setup a Debtors control account default, you need to tick the ‘Control’ tick box to use the account and the ‘Sale’ tick box for the Debtor ledgers. This option is only available for the account type of Balance sheet.

Please do take care to not untick either of these boxes after the account is set as an account default as this will affect where documents show on your ledger and control account reports. No further ticks are required for this to function as intended.