Turn off Overscan in Altirra 2.10

I'm playing Jumpman using Altirra 2.10 and with overscan on I get a large purple area at the bottom of the screen.  The only way that I can find that controls overscan is here:

View -> Overscan Mode

Currently the overscan mode selected is "normal."

I don't want overscan on at all.  I want Jumpman (and all games for that matter) to look more like it would on a real TV-- where you're lucky if you can see any of the overscan area at all.

I've searched the help and used Google to look for a way to turn off overscan completely.  I can't figure it out.  My simple question is:

How do I turn off Overscan in Altirra 2.10?

Adam