Hmmmm... I haven't really run into the chalky problem with them, so it's hard to say what I'm doing differently. When thinning, my wet palette adds a bit of water and then I might add a drop or two each time I mix the color for an additional layer, but I'm not thinning them down dramatically. If you are working with thinner mixes of the paint, you could try adding a bit of matte medium (and a little less water). That can help the paint behave better when thinned.
The other thing I could think of is the colors you use for highlighting and shading. For highlighting, I rarely grab the pure white. I got the green on the orc to go pretty light with a 50/50 mix of Meadow Green and Surf Aqua and then added some Ghost White (basically a very light blue) at the end. Other colors I use for highlighting are skin tones, vampiric skin (an off white), linen white, etc. On the shading side, I tend to avoid just dark versions of the main color. So if I'm painting green, I might choose a dark purple to shade instead of just using a dark green. For the orc I chose a dark blue (Ritterlich Blue) to shade the green. For reds, a dark purple or dark blue can work well too. For blue, maybe a dark red. You can see from the orc pictures, the shadows don't exactly look blue, but the variation in color creates a more interesting look. If the mix is just dark green, medium green, and light green it can end up looking a bit flat.
Here's a look at the colors I used for the orc skin on the palette. It goes from 50/50 Ritterlich Blue and Peacock Green (on the far left) to 50/50 Peacock Green and Marine Teal (near the middle) to 50/50 Meadow Green and Surf Aqua (3/4 of the way to the right) and then Ghost White (on the far right).
View attachment 59127
Hopefully something in there is helpful!
