I'm not sure I understand your method. Would you care to provide an exemple, I'd be interested!
Well it is going to be a little hard to describe. But if we work in greyscale bitmaps then to make a seamless texture you can use the tutorial thing I wrote a while back:
https://www.cartographersguild.com/s...ead.php?t=1373

Now if you do that only with 16 bit height map values instead of bitmaps then you can get the same result.

So I download a load of real height maps and place them together as best as possible. Then blend them into one large one where there is no obviously large discontinuities at the edges so that you could butt them together and it wont look all that bad. You can fade out at the edges and have a different tile if you like is another way to do it.

So that tile makes your high frequency rock texture in height map. You then manually use an airbrush to generate a greyscale bitmap of where you want your mountains and set up the heights manually but very roughly. If you want a long mountain range you can spray on a line of white and fade it all down so its a blurry greyscale height map of the landscape but with no texture to it.

Then with a suitable height map tool (and thats the issue usually) you multiply them together and then where you have high blobby bits you get high rocky textured zones and where it was low (or dark) blobby areas you don't get very much of the texture coming through. When you look at the result you will have mountains that match the form of where you placed them. The detail of the mountains look real because it came from real height map relief from earth data such as Shuttle SRTM or similar.