Pretty short game, but I just wanted to post this to show that upgrading mex to tier 2 is rarely a good idea on small maps like this. You don't really gain anything from doing so. You lose 900 mass worth of units, which means that you lose map control, which means that you lose mex and that +4 you get doesn't really cover the cost. I believe that this was the sole reason I won.
While upgrading, the mex is using -10 mass for 90 seconds, meaning that I can have an extra 2.5 factories working, which will give me an obvious advantage. Using that advantage, I can easily kill at least 2 of his mex, meaning that his +4 that he gets from the t2 mex is negated. And if I build those 2 mex, then it actually comes out as an advantage for me. Also, having the ground force advantage naturally puts me in a better position to reclaim after battles. It's just not worth it in most cases.