To be honest, I'm not sure what you're trying to do. But in the MAT Lab, when you edit the texture (using Editor - NOT Texture Source Editor), you get three sections - size, rotation and position. Position (the square with the 6 arrows) governs where texture appears within an object. Maybe it's this that you want????

AB altitude blending is based on the tallest object in the scene (doesn't matter if it has the same material, which is a serious limitation IMO). You'll want an A-B-C blend where C is used as an alpha channel and where C is black will be texture A and white is texture B. So your C will be a graduation from black to white and where you want B to start (assumed to be the "loud" texture) is where the blend will take place. Hope that makes sense.

Thanks Aldaron could't figure out how to get a shade of grey with only the alpha turned on. You need an altitude filter (fire from basic is a good starting point) and mess with the settings