Possibly you’re trying to run the same qty of strike and sparge liquor through a lot more grain in an attempt to get a high OG. That’s asking a lot of the mash. Efficiency is subject to drop when brewing bigger beers in one mash.
To help, you could split the mash grains equally into two more pedestrian mashes using a reiteration technique: drain runnings and sparge mash 1 as normal. Then empty the mash tun and fill it with the second half of the split grain into mash 2 but instead of using water as your strike and sparge liquor use the runnings from mash 1 to strike and sparge.
In another effort to save space in the mash tun, you could also mash only the grains that require mashing, steep the grains that don’t, and add the steeped grain liquor to the the strike or sparge liquor of the second mash.
Just some food for though.
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