I found in laying on a decal (let's say for cobblestone) it would sometimes not take in the smaller patches- leaving them gray. But sometimes, it would- it seemed almost random. I tried a small decal (1000x) and a huge one (3000x) and got no difference, so I don't think it's an interpolation problem. Tried TGA, BMP, TIF. Same results.
I even redid the splines in those "problem" areas, by laying in all new ones to ensure I hadn't connected them badly somehow. Still got random results.
And yes, I checked the normals and eliminated any hooks that may have been at fault.
The workaround I came up with was "fixing" all my geometry: widening the narrow patches as much as I could- while this compromised my model a little, at least the decal shows up!
It seems like patches for a decal must all be of a certain minimum ratio in size to each other in order to get consistent results in decal applications.
Anyone else encounter something like this? If so, did you find a workaround better than mine?