Polypro bags shouldn't be the culprit. Honestly, the problem might just be that the FOs aren't strong enough. I use BCN FOs mostly. Spiced Cranberry, Vanilla Grapefruit and a couple others. Love Spell from CS works good and Peak (Keystone) Midsummer Night is a good one too. You just have to keep testing until you find something.
Like I said before the stronger ones in other applications might be your best bet.