There is no "standard" mandating that a hover be performed "using a cross legged vertical position". A diver may use any position they like, as long as the standard is met that they "Hover using buoyancy control for at least ______ [insert time frame here, depending on course] without kicking or sculling."
Thus an Instructor or student may hover upside down, sideways, whatever, as long as they demonstrate mastery of the hover by not kicking, sculling, or moving up/down in the water column.
I agree, and I would like to talk about the trim issue for hovering a little.
The shop with which I worked had all OW students using BCD's and weight belts. It is pretty darn tough to hover in horizontal trim with gear like that. I therefore accepted any body position the student felt comfortable using for this part of the class. The key learning is breath control to maintain depth. I focused on swimming in trim during the rest of the class, when students could use their kicking to overcome the fact that their weight is not distributed properly.
PPB is a good time to work on the next step.
Hovering in trim, such as you would be expected to do in a DIR Fundies class, is a pretty high standard for new OW students, especially if they do not have the proper gear for it. I do not require that.