No - the gap under the frets isn't indication of a fault per se
The fret slots are probably cut when the fingerboard is still flat and they are all cut to the same depth.
When the radius is applied to the board the camber gets lower on the edges the higher you go up the neck
Think about the arc of a circle which is what a fingerbord essentially is
If the centre of the fingerboard is the top of the circle - if you follow the circumference the further you move away from the top/centre point the lower you get going downwards
So if the nut is 43mm wide - 21.5mm from the centre point you will have dropped less than at the 22nd fret end (poss 57mm wide) which would be 28.5mm from the centre.
Confused? - draw a circle and trace the changes as you move away from the centre/top
So these slot depths has no standing as far as the thickness of the neck goes IMO - although I wont say that Warmoth don't or can't get things wrong at times.
Is the problem that the neck is too big/clublike at the 1st fret area ?
You could just shave some off the back - slightly change the taper so to speak
However
Yaknow that makes sense. Sorry not trying to be rude, you have been one of the most polite people on this forum, so "please"don't take offense. :D
The only reason I know this cant be the fact, is that I have another neck with the same specs, and they're completely different. Also this gap is not present on the other one and it has the same radius as this one.
I know what you mean - it is a bit frustrating
Trying to get to the bottom of the issue - what about the neck gives you problems or do you not like?
Is it too clubby at the low frets or too thin higher up
Does the transition just feel weird?
Does it play ok or is it hard to get a great action on the guitar?
It certainly is an interesting dilemma and made me think a bit about how it happened.
I was just curious whether it was a problem to you that you were hoping to resolve....