Seems there's a cloud base altitude bug in XP12. Eventhough ASPX12 sets cloud base altitudes correctly in WX-settings, the cloud base altitudes are 300ft higher than should.
Maybe, ASXP12 should fix this by inserting every cloud base 300ft lower to get them correctly in-sim.
It's pity when you see your destination has OVC001 but you know XP12 bug gives you OVC004 instead.