So there are two different things to think about - there's the focus, which is what you think it is, and there's the 'vergence,' which I think is the fancy name for what you're calling parallax. Because the headset isn't trying to project a 3D image (unless you're in 3D mode), there's no parallax - all it's doing is projecting two flat screens at your eyeballs through a focusing lens.
However, because the spacing between the screens is not adjustable, your eyes will always do some level of 'vergence' adjustment to point themselves at the screen, effectively going a little cross-eyed or a little in the other direction. In the beginning I felt like my eyes were a bit too far apart to use the headset comfortably, but a recent software update allowed you to adjust this by trimming a few pixels from the edge of the screen to adjust the position of the image. While it's not perfect, I think it's helped a lot. I've tested this by looking through the glasses with a mouse pointer on the screen while trying to notice at which distance I see just the one pointer, and it's roughly around 3m in front of me, which aligns perfectly with the focus distance of the projected screens.
On the question of actual focus - screen focus itself is actually adjustable on the Viture XR Pro to accommodate for glasses prescriptions, down to a -5.0 diopter. You can adjust focus individually for each of your eyes, and I think it's this that actually makes the biggest difference in how relaxed you can be when you use it. I was worried that I wouldn't be able to adjust it for long-sightedness, but I'm a +1.0 and find there's still room in the opposite direction if I wanted to adjust it more on the dials.
Hope that helps.