Lay up and schedule
I have often found that I get the best results with opals, by putting the clear on top. I have occasionally had bubles from the clear base rise to the top, leaving clear pin-points within the opal colour. I also have fewer problems with devitrification when the clear is on top. So clear above opal is now my practice.
I do my bubble squeeze differently – not that your method is wrong – lots of people do it your way.
I soak at 677C for 30mins for a 6mm project. Having done a slow rise to 677C, you do not need a whole hour there.
Depending on your desired surface, you might thnik about raising your 796C top temperature to 804C but hold for only 10 minutes. This should give you an almost flat surface.
I don’t remember whether you are using Bullseye or System 96. In either case you can do your annealing soak at 482C for an hour. Then to 427C at 60C/hr. Follow this by 120C/hr to 370C. If the piece is 6mm you can turn the kiln off then, but I normally control my cooling all the way down to 100C.
In short, I think you will eliminate your bubble problem by putting the clear on top and reducing the amount of time at the top temperature.