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.
You can shortcut sample sizes by using the damage range.

Example: Damage range is 90-110.

40% damage taken range is 36 to 44. 48% damage taken range is 43.2 to 52.8. This chosen range works out well, but it'll be similar to any range. Calculate the ranges separately, any number that falls outside of one of the ranges invalidates that range. The biggest advantage here is that samples with the buffs up are going to be much more difficult to obtain. You only need to write down max / min of incoming attacks and then need (probably) only one sample of data with the buffs up.

I'd also be very surprised if they additively stack damage reduction. That's just too powerful.