The Z actually has extremely poor highlight recovery, from my testing about only -10 highlights in Lightroom before it starts to produce false colors. A Canon 5D3 would've worked wonders here, especially if processed in Capture One.
You really do not want the histogram anywhere near the right edge, IMO Pentax should adjust the scale and add several stops to the left to make the histo more representative of the total DR, as it is you're only looking at the brightest half.
Right half of this chart is what you see when previewing your image, left half is how much you have left to recover in post. This is assuming you don't have shadow recovery enabled in D-range settings.
For reference, here's a really old photo that I've kept just to test highlight recovery on the 5D2, it's over exposed by about 2.5 stops.