Protection values

[Embis]

From the manual:

When a hex contains Craters and does not contain any fortification or cave,

then infantry units get an additional protection value determined by the Crater
Protection Parameter Data value.

A couple of questions relating to this;
Not sure how to read the above if there is also a fortification or cave in the hex, does that that provide cumulative protection? 
so terrain protection value + Crater protection value

And:
 
Destroyed Terrain, 
does destroyed terrain lose its protection value? I note in the scenario editor it is possible in any single hex to destroy terrain, crater terrain, and add an improved position to that hex..how does that effect the protection value of that hex?