I would lean towards the defoamer too as I've seen that stuff not mix well and get stuck in strainers.  If you were bent on using the stuff a tablespoon or 2 for your tank should be sufficient. 

Dawn does help a little.

Are you running this stuff through an inductor or just dumping in the tank?  Inductor does seem to help it mix, but maybe that's just in my head an what i'm used to. 

I would also not wait until the tank is half full, put some water in and get the chemical in there, then finish off with water. 

Get rid of the nozzle screens and put boom section screens on.  I have a 50 mesh main and 80 mesh for the booms. 

GL on the palmer.