Much thought later...

I've reached the conclusion that my compressor is too 'thin'.
Although it reaches the required pressures, it doesn't deliver enough volume of air.

I've tried to calculate the dimensions but this is an area where the treatments presented in both Kamp's and Schreckling's books are very vague. Although there are several pages of math, when you read through them carefully they make little sense. The symbols used don't always correspond to the diagrams and formulae are often presented without proof or reference.
I suspect the translation in both cases, there's no excuse for swapping subscript symbols between 'th' and 'w' in mid-argument. But it's just the sort of typo you would get if the editor didn't understand the subject.

Whatever; Although it's possible (with difficulty) to calculate the blade height for the compressor wheel from the shaft power and other dimensions, the result relies so much on assumptions as to be almost useless.
The probable error due to 'unknowns' in the calculations is wider than the operating tolerance of the engine.

I will have to experiment.
The KKK compressor used in Kamp's design has a tip blade height of 5mm. whereas Schrecklings is 8mm.
Mine is 6mm. I will try making one about the same as Schreckling's.

Unfortunately, that means I will have to remake the entire diffuser assembly too.
Still, it's a chance to use that aluminium ingot I made.