You just mix up 258 g EPK and 240 g silica. Add incremental amounts of that to the glaze. You have to decide about how much ....so about 6% of the mixture will move it up a cone or so.
Conceptually it is like adding 1 EPK and 1 Silica. So you would add 1%EPK and 1% silica then test, 1% EPK 1% Silica for a total of 2% each, then, 3 etc.