Ok. So I'm new, green new, but I've studied a ton load for a couple months before diving in. I'll do my best to help. So from my experience, 20% co can be drying to some, and definitely can be drying to many at such a low superfat.
But the skin reportedly feels fine, not tight or irritated, which is what I would consider "drying" - so I'm still wondering if we're barking up the right tree.
Superfat it's above and beyond what you leave on your skin in way of un saponified oils. You sap the oils and fat with lye, and excess gets left behind to moisturize.
Picky point maybe, but soap is to clean, and will not moisturise. Oil doesn't moisturise either. Moisture (water) does. Oil prevents evaporation, and provides lubrication. You can either leave the natural oil on the skin with a low cleansing soap, or leave a residue on the skin with a superfat. (or both, I suppose, but for me that feels awful - I know some people love a highly conditioning soap, though.) That's called "conditioning", but not "moisturising".
I think I would still suggest the same things though. Exfoliate to see if the ashiness is just dead skin sloughing off rather than the soap drying you out, try a slightly higher superfat, don't worry too much about the coconut percentage right now, since your skin isn't tight or uncomfortable, and change one thing at a time in your soap (make small batches) until you like what you are producing.
Just my thoughts as we explore the situation!