letub,

One of the complaints I've heard about the wisker biscuit is that it can mask a bad tune. Some have the opinion that it shoots a good paper tear, even when out of tune. I've tuned many and have never had the problem you are seeing.

It looks like you're getting a slight low left tear from your qt800, almost opposite of the wisker biscuit. I would check to see that no vane is hitting the bottom of the biscuit, or any part of the riser after passing through.