At least you are showing a considerate attitude by asking (and they are showing their ignorance or arrogance by parking so close).
25 metres seems a bit much space to leave but it will depend on the type of fixed wing as well. Some very light or very low wing loading types could easily be damaged by R22 downwash at some distance.
What do others think is a reasonable distance to park and R22 from other R22's?
Ian.