I will be pressure canning for the first time and found a recipe from ball (the jar company) to start off with. My question pertains to the water level which the ball recipe does not address. Should my jars be fully submerged in the water, or can the water level be about halfway up the jars (not fully submerged)? What would the difference be? I will be canning 7 quart jars in my Presto 23qt. pressure canner.