During my all grain brew yesterday I realized that I had quite a bit of space between the lid of the MLT and the grain, I'm calling this head space. I measured that area to be about 10 inches and during the 90 minute mash lost a few degrees and am curious if this space could be the reason. In the future I'm planning on making a lid out of styrofoam wrapped in aluminum foil to cover the grain to see if this will hold the temperature better.
1. Am I on the right track thinking that this space should be minimized in order to control the internal temperature of the MLT better?
2. Does the make shift lid I described above sound like a reasonable solution?