The Elemental Type is actually quite clear, which is surprising given WotC's track record. It was really created for one specific monster entry, and has absolutely no problems as long as it is confined to things sufficiently close to that monster entry. The D&D designers extended it semi-humanoid things like magmins, which leads to a bit of confusion. But, we're going to run with the literal wording of the type here. Magmins and similar creatures aren't actually really humanoid at all except in the most basic shape, and their eyes aren't limited to only seeing in front of them. They don't even actually need their eyes. Like all other elementals, the inside of a magmin is pretty much undifferentiated elemental matter; in a magmin's case, they simply bleed lava. They are completely different