I've read a lot about these before I got my Tenpa 1.36x, I don't wear glasses but it already vignettes for me and it needs a tiny bit of moving around to see the edges. I probably wouldn't go beyond 1.2x if I wore glasses.

Seeing this is a K-r, could this be a case of artificial light inaccurate AF?

I had a K-r for a couple weeks before I swapped it for a K-5. I never managed to get a good focus indoors below f/1.8 with my Sigma 50mm f/1.4.
It front focused beyond the focus microadjustment range, but not in daylight.

These are recut canon ee-s screens.

This is the one I have.
I can't really vouch for the other screens but metering seems to remain fairly accurate with this screen at wide and not so wide apertures.

There was talk of failed center spot focus with split screens earlier. I think this was a confusion, split screens tend to totally mess up spot metering, not focusing.

If you like the FSL then maybe the K3 would suit you. It's not 45° though.

I got an EE-S for my K-5 on focusingscreen.com
It's also available for the K-r
"K-r S TYPE Focusing Screen (AF Frame)"

It's a massive improvement over the standard screen for my wider aperture lenses, and manual focusing is much improved.

nb: It's not split, just simple ground glass.