I have read Tammy that some like to do that jam and boiling water mix and stir/blend over heat on the stove, I guess that would allow you to add mor water if need be as you go, might depend on how much glaze you need.
I just mix in a glass jug to what looks right as jams can be different thicknesses and I don't do a huge batch...... but must be glazed as soon as it's turned out of the pan.
Have fun