Axe -20% mining quality stat

[LaserSaysPew]

What does it do exactly?
At first I thought the resulting stone/ore will have it's quality reduced by 20%, but it doesn't seem to be the case.

Mining the same node:
Axe q91 drops q49 wine glance
Pickaxe q47.4 drops q48.2 wine glance which corresponds to it softcapping q49 node.

So what does that "-20%" mean exactly?

[stya]

your axe counts as q91 * 0.8, this is then used as a softcap on the node q