Do keep in mind that REs do explosive damage, which deals +20% extra to armor, so with the low shields of the Gallente, a lot of the damage is bleeding onto your armor... and honestly, remotes do more damage them most heavies can stack EHP.

So, the tooltip on REs in the marketplace definitely says they do splash damage. I know before 1.8 REs were doing explosive damage as you said. I thought the mechanics were changing to allow sentinels to "stand and deliver" as it were. Perhaps they did not and my 25% reduction is to a nothing damage class, like being resistant to poison.

My stats on my favorite 9k ISK standard sentinel suit is 487 Shields and 750 Armor. for a flat HP of 1237. Considering explosive damage does +/- 20% that would be an EHP of 584 shields and 600 armor. So that makes sense. Out of the 1500, taking the first 584 off, and multiplying the remaining 900ish damage by 1.2 against my remaining armor would be right around 1700 damage. But that is not taking my 25% splash damage reduction into account.

So whether it exists or not, the splash damage reduction is not being applied to RE damage despite their damage being labeled as splash. For the sake of comparison, Locus grenades are also labeled splash damage while mass drivers have a direct and splash component. I'm guessing I shouldn't expect my sentinel DR to apply to either of those.

It makes me wonder if I get the bonuses against rails, etc. If I do, it may be that RE damage isn't applying correctly. If not, then perhaps sentinel bonuses aren't being applied correctly.