nitpick: there -> their (applies to all appearances of there in this file except the first).

*combinations
*corresponding

*functions

Have you thought about using a smart pointer here? As they are commonly used throughout the library, I would suggest to use them here as well for consistency (and obviously all other perks that come with smart pointers).

*keep

I suggest sacrificing conformity with maxis code in favor of readability/performance. I think something like

Type_t diff = A-B;
return diff > 0 ? diff : -diff;

or

return std::abs(A-B);

would be better here.

But this is just nitpicking again. This function is obviously readable enough, I just want to make a point that the reason we are reimplementing is to do it better than maxi ;)

Heisenberg would approve

*Calculates

Why is the operator() not implemented? Is that done somewhere else? Am I missing something?

Could fuzzyAND from include/rosa/support/math.hpp be used here?

If you use fuzzyAND and fuzzyOR, I think you should move this to include/rosa/support/math as well, so we have a collection of combination-methods there.

Could fuzzyOR from include/rosa/support/math.hpp be used here?

Most comments from CrossReliability (including spell-checking) also apply here.

Why define this twice? Couldn't a single function be used both for CrossReliability and CrossConfidence?
At this point, I would suggest deleting this function completely and use std::abs(A-B) wherever it appears. You could use

using std::abs;

and then just write abs(A-B) which reads as absolute-difference, which is exactly what it does. I think it does not get much more readable than that.
The only disadvantage that I see is that the assert would be missing, but std::abs is only defined for arithmetic types so that would be checked at compile time as well.

*evaluates