When the transactions are imported, if you delete them that would be enough to keep the figure down.
What you may find however is that it’s not just the bank boosting it up. There is a little report you can use to see where the most activity is:
http://community.quickfile.co.uk/t/important-changes-affecting-large-and-extra-large-accounts/8260/134?u=qfsupport
If you account does hit the L category, you will be notified and have a chance to defer it for 3 days before upgrading.
I hope that helps!