Bit of an update, even though my lovely strom is for sale.
I swapped back to the MRA vario touring screen that I previously had fitted, but made an adjustment to the way it was fitted. I've put it on the lowest mounting point (as I have with all my screens), and then obtained longer bolts and various spacers.
Now I have about 15mm of spacer in the lower two mountings, and 5mm is on the upper two mountings. This angles the screen towards me more, so much so it couldn't actually angle any further without spacing it off the bike further.
This has made a surprising difference. The air is now smooth! I took a spin up the motorway, and it was much improved. Helmet now in clean air.
There's still a little noise from the screen, but it's smooth noise if that makes sense.