Playing devils advocate here, if this was a pole height issue, there would be variation across all strings. The output is governed by the size of the steel moving within he magnetic field, and the strength of the field. The strength would be varied by the distance from centre.
Ok, the e string has a bigger gauge string, so this may account for there being no issue with the loss here. But surely there should be a noticeable difference between the A and D strings also due to different string gauge??
The same argument could be made for any pickup guitar or bass that has varied pole height? Think of a guitar with an .009 high E where the poles are contoured to suit the neck radius? It doesn't seem to be an issue commonly reported.
I haven't noticed this on my sterling bass, haven't noticed if the poles are varied on this bass, but it does have a 3 band eq.
Is it only 2 band eq rays that are affected?
Is it possible that there is just some frequency cut/cancelling happening in this range only due the native circuits of the amp/bass??
It be helpful to build a database of who is using what amps with their ray and what model!!
I genuinely feel for anyone having this problem, stingrays are just amazing basses. Everyone deserves to enjoy it as Leo intended.
Personally, I have used a USA SUB5 with my gallien Krueger rb1001ii with neo 212/115 and now using my stingray5 with a markbass TTE 500 into gallien Krueger neo 212.
I have used the sterling bass into the markbass/neo setup but only for practice at home, never in a band setting so this doesn't count.