I'm sorry, but where do you come up with this theory about a lack of mixing in commercial horse vermifuge? Any company that would produce such a thing would go out of business faster than Donald Trump! Not to mention the regulatory problems and veterinarians who would drive any outfit producing such a product over a cliff, PDQ.
With all due respect, barring you providing some kind, or even any, actual evidence for what you say above, I will disregard your anecdotal and quite likely misleading observations.
edit: I forgot to again thank you casportpony for your diligent efforts at making deworming our birds so much less of a daunting task. Your math is spot on and advice worth it's weight in Zimectrin Gold! (Called Eqvalan Gold up here on the northern fringes of the civilized world)