OK, so Volcano is a neat idea for a map, but everyone complains about it because it's so feverishly unbalanced in the humans' favour.
I suggest that the blue force field that currently surrounds the summit be replaced by a rock barrier, so that the human base is located not at the very top of the volcano, but just inside the mouth. As well, most of the platform should be thinned, so that humans only have a limited area in which to build the bulk of their base. There should be an area opposite the human base which is shielded by rock, that the aliens can hide behind.
This is an improvement because it will allow aliens to wallwalk up to the human base, as well, the thinner platform will limit the amount of control the humans can have over the summit.