Quote Originally Posted by Kitru View Post
Are you sure? Most other simultaneous effects in ARR are multiplicative with similar buffs, not additive. Given the nature of damage ranges and the similar levels of mitigation you'd achieve from either additive or multiplicative mechanics (additive would put you at 40% damage taken; multiplicative would put you at 48% which is well within the range of damage ranges suggesting identical results), unless you have a very large sample size, I'd lean towards Rampart/Sentinel following the existing pattern rather than being a unique case.
I'll give it a shot again since i ddn't record it properly, but I am very sure that Shield oath is multiplicative towards Sentinel/Rampart.