Finally getting coturnix quail!
Most people I have seen comment about coturnix have said that they do not nest (at least not usually). They just drop eggs wherever they happen to be standing. They also apparently are not very good about going broody or incubating eggs if they do happen to have a preferred laying location. So your nest box at 4 feet off the ground is probably not going to be used by anyone.
I have seen a few videos where people had nest boxes that were accessed via a ramp, like you see in chicken coops. Apparently you can train them to walk up and down a ramp.