So, to match a diffuse texture with the stencil height-mask, the mask must have been created from the diffuse texture.
When using a brush, from badking-site, you will have a height map for alpha, but no matching diffuse texture.
Hmmm, hard to explain.
Maybe look at the pre made stencil brushes in beta 10.
Take frog-belly for example. This brush consist of a diffuse texture, height alpha and so on.
Now, when creating a new one, you got alpha, metal, roughness, but no normal or diffuse texture.
Best regards