IMAX is a shallow marketing gimmick and always has been. There’s a reason cinema settled on a frame about twice as wide as it is tall - that’s how humans see the world with two front-facing eyes side-by-side. If DV wanted more of Chani in the frame, he would have put more of her in the frame.
TL;DR - you DON’T need to see Dune Part Three in IMAX. Spend the money instead on seeing it in the best auditorium you can - preferably with a laser projector.