I actually do know where the hex-sphere came from. When Wanda and Pietro came back to the Avengers, Roy Thomas was also writing the Hulk's book, and for some reason he introduced his new idea about Wanda's powers in an Avengers guest appearance in
Incredible Hulk #128 (where, apparently, Wanda has never bothered to test her power since she got it back in
Avengers #76).
Roy's new definition of her power is that by putting both her hands together she can send out a "hex sphere" that alters the probability around anything it touches, but Wanda can't fully control what will happen. It's like a floating random probability-altering field or something.
It was a bit awkward to draw and another example of how Thomas, like Mark Gruenwald, seemed not to want Wanda to be too powerful, but it lasted longer than Roy's new idea for Quicksilver's powers, where he could bounce around like a human pinball.