Well in the original *A layout, you ahve 4 mexes in your starting square, 2 on each of the platforms and like 10 in the center.
Each spot gives +5
Evo works differently because in evo, every mex gives 0.5 period. Evo is designed for a 5 mex start and metalmakers are a legitimate strat in evo because energy is used to fire. One mm gives +1 metal, but drains -10 energy (nuclear powerplant provides +10 energy), which is a pretty big deal.
Your energy pool in evo to start with is only 250 and in a battle, that 250 will disappear almost instantly, so when you're using mms, you're having the tradeoff of energy consumption and losing the ability to stay in a pitched fight as if you run dry, your units won't fire.
So, I say all that to say this...
Evo layout is 3 in your start square, with 2 close to your square up above on the platform on either side (so potentially 7 spots nearby), with 3 in the loading zones and about 10 in the center. Keep in mind, build ranges for units in evo is huge.
The evo layout mexes will give +2 apiece for non-evo games.
Hopefully I explained that so that it makes sense
