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The 5x20 cone 6 glaze at cone 9! Yikes.
Normally high fire glazes don't employ boron, it is not needed. It is known for this issue also.
You should be able to use a boron free recipe, or at least one that only has 5% frit (to get it melting earlier). How about our G1947U recipe for your plate shapes.
With all that EPK the glaze does not need the bentonite. That adds drying shrinkage which can loosen the bond between glaze and body. Not using it enables use a thixotropic glaze slurry, which gives better applications properties and better adhesion.
https://digitalfire.com/glossary/thixotropy
That being said, maybe there is a way to get your current glaze working. The hold needs to be done at a temperature where the glaze has stiffened enough to break any blisters but is still fluid enough to heal them (and pinholes).
That means lower than 2200, a lot lower. Try 2100 and 2050 or 2000. Because the glaze has been melted so high, it is likely melt fluid at a pretty low temperature.
Buy me a coffee and we can talk