Flapless on a P28 takes too much runway, and is not recommended in Spain with its temperatures.
Flaps 25 for short field is indeed the correct procedure. I know that 10° is not mentioned in the Handbook, but that does not say that it is not an approved setting... By the way, Oxford uses the same settings I've been told by an ex Oxford guy.( can anyone confirm) Anyway, it is good practice for the students.
Our ASI 's are in Mph on the Arrows.