DracoSuave
First Post
DMG said:All the information the players need to make their choices comes from you. Therefore, within the rules of the game and the limits of PC knowledge, Insight, and Perception, tell players everything they need to know. You don’t have to reveal all aspects of a situation or hazard in one go. You should, however, give enough information that the players know what’s up and have an idea what to do—and what not to do.
The DMG suggests directly that if your players have a tactical choice to make based on something they can legitimately perceive, you should provide them with that information. The skill put into an attack against them when they have a particular affinity for defensive mojo (i.e. they have a power) certainly qualifies as something they'd legitimately be able to perceive.
I don't need to tell them exact numbers, but if it's in Shield range, it's fair game to tell them, and if it is not, it's fair game to not.
You're dealing with a character with an IQ that must be above average and likely has Wisdom higher than 12 which makes them inherently perceptive. The vast majority of characters with Shield are smart and saavy enough to know the effects of attacks against them they have specific training to thwart. It's very reasonable for them to have an informed take on the matter.