I use the long metal chick feeders for mine. They can get their heads in the holes and scratch all they want...as long as you don't fill it any more than the top of the bottom pan they won't scratch it out. Anything with a 'bottle' or 'jar' is a waste of time, those just give them all that much more to waste.
They solve the #1 problem with coturnix feed waste. The endless supply of feed...AKA, the hopper problem. Pretty much anything with a flat bottom, where feed just doesn't fall out of nowhere is the best. The PVC feeder is yet to be evaluated by me, but I have that on my list of (things to do), to stop feed waste.
Providing a good quality and fully stocked "Dust pan", removes the 2nd problem. Dumping all that dusty 30% GBS on this wire floor so "I can take a dust bath". Not the sharpest tool in the shed, which is why you can out think them, and why you should never think that they do things just to spite you. There is something going on in that little pea brain, but not spite and malice.
There will always an amount of feed wasters as far as coturnix goes. There will always be that one joker in life, who's 27/7 mission in life is to pick out every speck of feed from the feeder and waste it.
The #3 (Cull option) must be deployed in that case.
Mine is 1 " but was thinking of going to 2. 4 " is quite large for their necks but I am the kind of guy that If 4" is what I had, then I would make it work.