With the way I set my neck relief, the action does not get higher in the middle of the neck. If you start looking at the string height at the first fret and work your way up the neck, it just ramps up a little earlier. It still gets higher as you go, but it doesn't get very noticably higher between the 12th and 24th frets.
You may want to play around with how much neck relief you use. I don't typically try and measure it, I just sight down the neck and look for a very subtle arc. I'll fret at the 1st and 14th frets and eyeball the string height, it should be very slight.
I don't know if this helps.