While I don't have Ermelo, if it's like other recent PG samplesets, you can mix levels by division and perspective. For example, starting with the Close Front Rear overall levels at 100, keep all 3 perspectives of the pedal division at 100% while reducing the manuals to 80 (just to try something, not a magic number!) to make the pedal stops relatively more audible. Adjust Trim to hear it well. Find the manual levels that work for you against the pedal.
Once you get the pedal and manual divisions in a balance you like, then you can change the overall levels of Close Front Rear until the reverb vs articulation compromise is acceptable to you.
Your speakers and room change what settings sound good, so there isn't some special formula. I mean, if Fey and Rowley give you their numbers, it may not sound similar on your system.