I think I have read that distance on a clean hit may vary +/- 15 yds.
When I play real golf the distance varies much less in the short game than with a driver.
Therefore I suggest that distance variation should be a percentage og the length you try to hit instead of a fixed yardage.
Read this as if your club can hit 160 yds and you hit 50% you try to hit 80 yds and the variation should be a percentage og 80 yds.
Tom.