I wrote this in response to an article written by Brad Smith in which he stated that one of the "cons" to brew in a bag was a high water to grain ratio. He didn't respond.
"You mention that a high WTG ratio produces less beta-amalyse. In my research the higher WTG ratio impacts conversion positively. The enzymatic conversion of starch to maltose for B-Amaylase is activated in the temperature range of 143.6 to 152.6.
See the following from Kai Trauser with references to Dr. Ludwig Narziss and Dennis E. Briggs."
The results for mash thickness were somewhat surprising. Contrary to common believe no attenuation difference was seen between a thick mash (2.57 l/kg or 1.21 qt/lb) and a thin mash (5 l/kg or 2.37 qt/lb). Home brewing literature suggests that thin mashes lead to more fermentable worts, but technical brewing literature suggests that the mash concentration doesn’t have much effect in well modified malts [Narziss, 2005]. Briggs cites data that doesn’t show a change in fermentability when the mash thickness is changed [Briggs, 2004]. This was confirmed by these experiments where all the data points were on the same curve that had already been established in the temperature experiment.

To keep the temperature drop between the experiments the same, the mash volume was increased and the result was a 2 degree Celsius temperature drop which matched the temperature drop for the 5 l/kg mash. But in the end that didn’t make a difference.
A significant difference was however found in the efficiency. The brewhouse efficiency of the thick mashes remained almost constant between 58 and 60% over the temperature range of the experiments, but the brewhouse efficiency for the thinner mash showed a strong dependency on the temperature and was always better than the efficiency of the thick mash. That leads to the conclusion that thinner mashes perform better and allow for better extraction of the grain. Briggs also reports that thinner mashes can convert more starch but that most of the conversion potential is reached at a water to grist ratio of 2.5 l/kg [Briggs, 2004]