re: Homebrewing - Weekend Recap

I am slightly confused by your question but lets see if we are on the same page.

You mash in with roughly 4.5 gallons of water at 165ish, which would take your 11.5 lbs of grain up to about 150. You let that sit for about an hour (length of time is debatable). Once that hour is up you start sparging with 170 degree water. Since you are fly sparging you attempt to have the wort draining at the same rate you are adding sparge water. The goal is to end up with enough wort that after your boil you have your target amount of wort (some people want 5.5 gallons into fermentor, some want more or less).

Depending on how well you did with your mash and sparge procedure, you should ideally get about 70-75% of the convertible sugar out of the grain which depending on your final volume will give you your OG. Towards the end of your sparge the wort leaving the mash tun is probably very weak, so typically you are just trying to get to your pre-boil volume.

The water does not act like a vacuum but rather a method to remove the water soluble sugars. So adding an extra gallon or so of water will probably not hinder extraction that much.