All you have to do, is do the Math after quick parsing a log.
Once you know what your shield damage resistance should be if it were Additive, when someone shoots, you you look at the log. If it doesn't match up to what the resistance should have been then it's multiplicative.
If you use the old equation that snix provided also, and the damage matches up to what you took then it's also multiplicative. Double confirmation in short order.
Took 2 accounts i have, (alt is for my fleet invites for main account).
Alt was a lv 28 using a Lv VI white DHC disruptor to shoot at the 50 admrial on my main in a Chimera. Set defualt sheild power to 100 and for the non-EpTS test i used a sheild bat to boost it from 118 to 125. EPtS did this itself in it's test.
Fired one salvo under each condition and did math, pretty easy.
One possability though is that sheild resistance per power is set on a per ship basise, that could mean it's just the chimera, didn't test the others, (wen tfor an afternoon nap straight after, just got back up).
Alright so if it is 25% resistance on a shield power of 125 and this is factual? Can we make the altercations to the wiki for this data? A lot of people referred to this (like me), to suffice the resistances on multiple builds I have been working on with Jedi Master Yoda, and a few others in TRH.