Painter 2023 Fluid brushes very laggy

Fluid brushes was the primary reason for upgrading to Painter 2023, but the experience has been very disappointing. No problem until you tick the 'Use Layering' tic box in the 'Paint Layering' panel. 

The idea behind this feature (I think), is to render very subtle, nuanced tonal ranges. Instead, I'm literally fighting with the brush as I try to render form and shadow. I've tried different file sizes and all sorts of variations. 

Nothing to do with my computer's capabilities, so let's not go there. C'mon Corel!