jgdsoarin,
I just got my Aliner last April, an Expedition model. I traded in my much loved and used Jayco highwall popup to get it because my two older boys have left the nest for college and my daughter will be gone soon too. So it's nice to know there's another Aliner owner out there. What model do you have?
The tent pads in the Tent/Partial sites vary in size - some are small and irregularly shaped while others are wide and quite deep. There is no standard size. We advise people if you are planning for a camper and a tent on a site to list the size of the tent as a note on the reservation. That information will flow downstream to a Fort Cast Member a few days before your arrival who pre-assigns you a site number based on planned availability and any notes (requested loop number, tent sizes, etc.). Unless your tent is really big (say bigger than 10x10) it should fit on most sites with an Aliner and screen room.
Lots of folks like 1500 over 2000 for its location so it can be hard to get into. 2000 has about 3X as many sites as 1500 also so the odds are not in favor of 1500. The thing you can do to help get 1500 when you check in if it's not been pre-assigned for you is to get there as early in the morning and request it at check-in. Offer to wait for it if someone is checking out that day. Of course that may mean you get a site that makes the tent-camper-room squeeze a little questionable.
I put this thread together a few trips ago about pad sizes in 1500 which may help.
http://www.disboards.com/showthread.php?t=2901476
Bama Ed
PS - WHEN you make a loop request makes no difference as long as it is on your reservation when it downloads for pre-assignment of a site number. If you add the tent size to your ressie, do it then. I think when you use My Disney Experience (the whole Magic Bands, FP+, dining reser etc) there is an "early check-in" option that opens up a few days before arrival which, IIRC from last time, included some limited loop request options. But I have always phoned it in or made the request when making the initial ressie and it was always attempted to be honored.