These are not optimised for fast newtonians. Bear in mind the european market which APM cater for is mainly refractors with flatteners, SCT and maksutovs, and Markus Ludes has a 16" mak.
And over small fields typical of eyepieces under 7mm field curvature shouldn't be an issue anyway.
Even with my my maks I could use 50 or 60mm eyepieces.