G’day goannadareyou,
We were going to use mini orb but instead went for aluminum checker plate in our shower (no bath). This was a few years ago, so things probably have changed, but I couldn’t find anything that would give a reasonable seal.
The checker plate makes installation a little easier as you can file off the raised areas around the installation points, giving you a flat surface to work against. I even decided against this in the end and went for a ceiling mounted shower rose and a mixer installed outside the showers screen, not much help in your situation but there are always 2 ways to skin a cat.
Just something a little different (it came on the market after I’d finished ours and I’d love to use it) have you seen aluminium propeller plate? not as many raised bits and its chemically polished
Brett