I would say it's closer to 30% for all the times I've tried it. Also, perception for appraisals is capped on chysahl at around 620ish, so as long as you're above the cap it should produce the results you've seen :)
I would put more faith in something like the following:
impulsive > (single mind if proc/discerning eye if no proc) > utmost caution > methodical > impulsive > (single mind if proc/discerning eye if no proc) > utmost caution > methodical
That would guarantee you get at least one with about 550; each proc of impulsive is another gather attempt. Good for if you're going for counterfoils, and if you don't mind a lower quality to turn in for red scrips instead, then i would use the other rotation i listed earlier.
But to each their own :)
