Undersizing a log fin.

So my local break tends to be VERY shallow for a lot of the ridable time as it approaches the beach. I ride a 9'8 traditional noserider, meaning a 10" fin and I find myself having to give up a good bit of the possible ride to protect my board. This sucks. Additionally, a new board is not in the cards right now.

Has anyone put an undersized fin on their log? I'm curious what the feel is.

Thanks for the help.