Every kit, every custom hot rod I've seen with an adjustable prop valve is as shown in the pic, not on the dash, not underneath in the frame rail (shield or no shield).
With fresh front and rear brakes, drums adjusted, bias is set at the valve, once you are happy with it, that's it.
It's not a height-sensing valve, it's not a replacement for one, it's not meant to be used as one.
I'll also mention, if you are retaining drums, when drum braking wanes, it's time to inspect and adjust or replace, if you are constantly increasing pressure, changing pressure, how will you know when it's time for service before failure?