Good to see a maltster paying some attention to the mill gap, its one of those really important steps on the journey from malt to good beer that usually slides under the radar.
Screening on a 2.5mm screen post malting and claiming an average plumpness of 2.8mm is exceptional, that's actually quite a lot bigger than most malts except perhaps some of the UK ones.
Worth noting that the information is only for Barley malt and wheat needs very different handling.
I would in a high wheat malt grist normally crack the wheat and barley fractions separately.
Crack the wheat at least twice often three times, first pass at 1.8-2.0mm, second pass around 1.4-1.5mm, then likely another pass at around 1.0mm. Then mix the wheat and barley and crack the mix, would agree that around 1.4mm would be good for the barley.
Wheat lacks a husk, is a different shape and is a lot harder than Barley malt, the aim of cracking wheat is to get a fine kibble and very little flour. With care you can get an almost dust free kibble that allows fast extraction, very good flows and little chance of a stuck sparge, all without needing "hulls" of any sort.
Without careful treatment, I find people get much lower efficiencies slow and stuck sparges...
Rye and Oat malt are other grains that need special attention. Treat rye like wheat, just a lot finer, miss the first pass and finish it at 0.6-0.8mm. Oat malt I tend to run first and on its own at about 0.25mm, just smash it as its got a huge husk fraction and doesn't crack as much as just spread out.
I have a little sift set with 2.0mm, 1.0mm, 0.5mm screens and have done a fair amount of work on grind optimisation.
Trying different settings and shaking down a sample, weighing fractions... all very tedious but if you think of a 10% improvement as giving you every 10th grain bill for free it really counts when brewing commercially.
There is an set of EBC standards for malt sifts and they are different to what I have, but sometimes you just have to use what you have, and yes it makes a big difference.
Depending on how much work your LHBS is willing to do on your behalf, making a lot of wheat beer might be the best argument for investing in a mill that I can think of. If you plan on doing a lot of wheat beers make sure you choose a mill that is easily adjustable.
Mark