David, I was just playing with the soft proof.
In my workflow, I use Capture One, then export to Photoshop or Affinity. My print choice is Mirage Print.
If in Photoshop, I softproof, make adjustments in another layer then print direct to Mirage.Photoshop ignores the softproofing when sending to Mirage, but keeps the corrections.
In Affinity, I soft-proof in a layer, make needed adjustments in a layer on top of the softproof layer.
I then delete the softproof layer,flatten and save.
Affinity doesn't work with the Mirage plugin, so I save back to Capture One, then drag the file to Mirage.
The colors appear fine using this method. I too use a color managed system BTW.
Oh and my entire workflow is ProPhoto RGB.