My service dog will not engage the helper in muzzle training?

I am a novice canine handler from a mid-sized police service in Ontario, Canada. I was interested in introducing my dog to muzzle fighting to help increase his fight drive as this was somewhat lacking. I purchased a muzzle, read several training articles, and purchased your training video on muzzle fighting. The introduction period to the muzzle went fine and I began the work in a circle with other canine unit from the area. His initial hits were fairly good, high and more or less in the right position, but not very hard, striking the quarry with his front paws more than the muzzle. To help increase the intensity of the hits I had the quarry use a sleeve and the hits were a lot harder and intense. My problem is now he won?t respond to the quarry with a proper muzzle hit unless the quarry has a sleeve on. He will act in an aggressive manner but seems to be looking for the sleeve. I am asking what I could do to get him back focused on the quarry and stop looking for the sleeve. Thanks in advance.