how do the terrain mesh layers work on fs9?

[CenturyHangar]

here is why I am asking this question:

I have FINALLY ultimated my ENTIRE USA SRTM terrain mesh installation and I also bought Ultimate Terrain USA...

I thinkk they are working together but I am starting to have doubts... how would I be able to tell if UTUSA has replaced parts of the terrain mesh? and does UTUSA do that at all???

[microlight]

Normally the most recent additions to the scenery library have priority. So if you have scenery A installed there, and then put in scenery B that covers bits of scenery A, then those bits from B will take priority and be displayed in preference to the same bits in A.

[CenturyHangar]

so what would be best to have on top? SRTM or Ultimate Terrain USA ??