I let them know what they missed by.
In my mind it's not too powerful because they may need a 5 or 6 on the 1d6 and could roll low, their risk, their call.
I do think that the DM needs to learn how the group works.
If they are (like we are in our group) interested in what HP an enemy has to the point that when we add up the damage against him (say 25) and the next hit does 5 points (30 total) that puts him bloodied, we know that he wasnt bloodied at 25 but is at 30 so his total HP are between 50 and 60 and he has between 25 and 30 HP left.
This annoys our DM a bit but due to the design of Bloodied in the game, it is unavoidable and players will do it either activly or passivly in a lot of cases.
Also if you hit an opponent for 16 vs Reflex and it misses but another guy hits for 17 vs Reflex and hits, you know that the monster has 17 reflex... it often won't help you since you are going to be at the whim of the dice rolls anyway but sometimes knowing that the same enemy has 22 AC (judging by previous attacks that miss/hit) and 17 reflex, focusing on attacks that hit reflex instead of AC seems wiser.
This could translate tactically into the adventuring group analyzing their opponents to see where they are vulnerable and such but to some DMs the groups ability to peek behind the screen can be a bit unnerving.
I think that if some Devas use this cunning to assertain what hits and what doesnt, rolling a D6 in instances where they believe due to the information gathered in the encounter seems fine and even in keeping with the game but to use the roll as some kind of mulligan type do-over seems a bit overpowered and I dont think at all in keeping with how the game is.
Oh and appologies... It seems I have necroed this thread quite badly, it is over 2 years old!! oops