... No matter what, the equater is going to be the largest strip of similar climate. ...
Only on a map *with* an equator
I haven't caught any word about the current map options other than what BoogieBac said in reply 2: "...flat and non-square..."
So, having an equator might be an option, or an equator of some sort might be a result of choosing an option or set of options that sum up roughly as Has Two Polarized Regions at Center Top and Center Bottom. The polarizations could be complicated: opposed elements (e.g. fire vs. water); a divided element seeking to re-unite (e.g. flood the world); good vs. evil for a given element, etc.
My real preference would be to have the map generation options strongly reflect the back story, so we could have something like what you describe for when "the channeler's essence doesn't work as well near the magnetic poles because its too close to the dead heart of the world."
In other words, I want the story of magic in Elemental to be woven directly into the algorithms that generate game maps. Even if we can't see it directly as players, I want it to be there. There was a World Before the Game. Great Powers wrecked the world, and the current channelers have some sort of (Elemental?) connection to those powers of old. So whatever input players give to generate a map for a new game should run through algorithms that know the Shards were all part of One Thing, remember where that Thing might have been, have some ideas about how a few choices made by Great Powers might have gone differently, etc.