We requested full size the last two visits, but received camaros. Works for the two of us, even though both were canary yellow and we're wayyyyy too old for that color. However, they also offered Hyundai's smaller SUV. My impression on full size cars is that they work with you when you get there quite a bit. Those SUVs are kept on for people who need them but it seems like if nobody signs up for them, they put them out for full size reservers. I never want them, but I would say they are offered about half the time. TPA has always had an abundance of cars with all companies when we have been there, although not usually mouse time.
I would also consider getting a fast break account. Just saved a good 45 minutes in line last weekend at PHX, which was packed for the holiday. It would seem that if they could help you that being a frequent renter would assist your cause.
Finally, check for updated Wendi deals. Right now, intermediate SUV for $22/day. They had that same special at Christmas too for several months, so it reoccurs frequently and/ or gets extended.