Unvanquished is an open-source FPS game featuring team-based strategy and RTS elements, pitting humans against aliens in a futuristic setting.
https://forums.unvanquished.net/
What about instead of the arbitrary "Too close to the enemy to evolve", aliens turned into low-health (75?) cocoons for a few seconds before they evolve? Evos should be taken before the alien turns into a cocoon, so if you start as a dretch and try to evolve to a dragoon and die as a cocoon, you lose 3 evos.
But you could give a cocoon animation to an alien buildable. Instead of a growing structure you would get a growing cocoon and after the building would be finished the cocoon would burst open and ta-da the structure would be there. Would look much neater. 
Natural Selection uses a similar method, but works anywhere as far as I know as long as you're on the ground. (From what I've seen, I've never played it).
I love evolving into tyrant just before a human comes near to scare the shat out of them.