CW, I don't think there's an absolute numerical answer for you to abide by. Depending on your grass species/cultivar and how you want the ball to react interdepends upon soil, slope, compaction, traffic, irrigation practices, exposure, etc. Perhaps you have a severe slope that runs 30 yards from the green toward the fairway and you don't want the ball running all that way down to the divot factory, then the grass needs some length to control that.
My preference is the chipping / putting option game around the greens but I see most players use a lobby wedge from 5 feet off the green. I guess it comes down to the clientele though if it was my place . . . . "I'll tell you what you want !!!"