You can definitely snag a car off the Compact aisle without going inside. A more common application of this is an Exec member booking "up" a category or two...SUV, van, or even confirming a premium/luxury car. No need to walk inside to talk to anyone there.

Whenever I book a higher category than midsize, I always look at the Exec area as well as my confirmed category. But obviously with a compact confirmation, you're supposed to just take from the Compact aisle.

The mechanics of this were a bit confusing when I first started renting from National. I used to select compact in my reservation and apply a 1-category upgrade coupon, thinking that would effectively be midsize...and thus EA/ES eligible. An exit guard told me that technically I'm not supposed to do that...since the difference was always $1-2/day, I stopped doing it to avoid having to discuss it at the exit. Logically it feels like I should have been able to do that, but I don't really know.