I've had a problem with funneling. Short of filling it up, I take a yard stick & make equal before I cook. I take a shop vac & suck out all the dust from bottom of grill & burner pot before starting. I've shifted pellet before but have found very few residue. Biggest things is simple maintenance.
I don't think you're problem is from not sifting. I believe it's from the moisture in the air depending on how long you leave the pellets in the hopper. I have left a bucket of pellets just sitting in my garage and after time if you sift through them with your fingers you can see and feel them just crumble like sawdust. Not all of them but enough to cause a problem.
