The perception passive skill doesn't actually increases HQ rate.
What it does is show you the perception threshold to have an HQ chance at that particular item. It's not so much a buff as it shows you more information.
Once your Perception value crosses that threshold you can gather HQs of that item, the HQ chance is a function of your Perception value and your level in relation to the level of the item you're trying to gather, capping at 15%.