First I would forget that weird measure above you bust and add 5" nonsense. If that was true we would all be a 42 A and we are not. Ask any professional bra fitter and she will tell you that most women wear a band size that is too large and a cup size that is too small.
Interesting fact one: If your bra is uncomfortable and you always feel you have to haul the band down, you band is not too tight, it is actually too loose. A smaller band size will stay put and therefore be more comfortable. In my own experience after my very expensive bra fitting experience the band size that fit me in the end was very close to the actual measurement of my chest under my breasts, in fact the band measure was the measurement of my body where the band would be, funny thing.
Interesting fact two: the size of the cup goes down as the band size increases. This means that a 34D has the same actual cup size (and of course underwire size) as a 36B and a 38A. Just pause and think that one through. So if you feel your cups are sort of baggy in a current bra, you might be better to go down a band size with the same cup size than keep the same band and a smaller cup.
So maybe your "fitting" issues are wrong size, lack of information, issues.
Interesting isn't it?