Yeah, calibrating the battery would essentially just give it another cycle. Won't really do any good.Last month I see that the iPhone drains faster then before. So I just check the batter health. I will try to calibrate it, but I think it will not help.
On a sidenote, I think Coconut battery is one of the better battery measurement assessments out there.The overall capacity can fluctuate. Be sure that the Phone is not too warm when check for battery health. I got 82% on my 6s back in January, and now it has got 87%.
Similarly, my new MacBook Pro seems to range between 93% and 96% all the time.
PS. I'm using Coconut Battery