Originally Posted by
underdogba
It is multiplicative, which you can confirm by blocking any attack with Divine Protection or Guardian up, then looking at the combat log.
With respect to the mathematics, the point I'm trying to make is that in stacking Holy Shield with other cooldowns, you are sacrificing a percentage of its efficacy in damage input / second. There needs to be a very specific reason in an encounter to be doing that, which does not justify the blanket statement in your original post about the subject.