as for why this isn't an issue with your travel agency bookings, I can only guess that the name on your profile matches the name on your MP
account, otherwise they'd get an error from the system and your MP
number won't take. As for the issue at hand, a couple of ideas:
Want to avoid india? call international res, you won't get India. Most of the time International will be glad to help, even if the res is domestic, if they ask you why you called them and not domestic, just explain that you're trying to avoid india, they seem to understand that sentiment.
When you make reservations online, have you tried putting both your first and middle name in the box designated for your first name? like firstname space middle name.
Finally, unless you have a hypenanted first name like John-Paul or whatnot, try calling the UA
milleage plus service center and have them take your middle name off the account. they should be able to do that and it might eliminate alot of headaches when it comes to trying to get the system to recognize your status and let you select economy plus seats online.