You are fly sparging with a HERMS set up? If not, that sounds very tricky.On my Brew-Magic the suggested method is to;
Add cold foundation water to MLT (that is, fill the deadspace).
Backfill MLT to 1-2" above grain bed.
Rest for 5 minutes.
Stir to eliminate dough-balls.
Heat and recirculate until desired rest temp is achieved.
It's a little un-orthodox but, I like it. Still working out the efficiencies.
Close enough. It's a RIMS and yes, I am still working out the sparge volumes. On average this meathod seems to yield a strike of 1.3 to 1.4 qts/lb.You are fly sparging with a HERMS set up? If not, that sounds very tricky.