Well,
I compared them, taking them as two separate races.
There is a difference - albeit small.
Observe:
http://i.imgur.com/qP3GJ1m.jpg
The two dots are missing from the UP.
It might be an oversight of the art team... who knows?
From what I have seen the other head of the UP(the smaler one) is an exact copy of the UA head, except colorization. I think it safe to say that the 'thorax markings' are the same on both.
There are tons of speculation on the markings in thread one. We never had a definitive answer. Keep looking. There might be a system to this, after all.