Since the book is also on Google Books, I was able to copy a table that shows some interesting data which can be explained with aforementioned enzymes:
It lists the attenuation limit (fermentability) for 2 sets of mashes done at different mash thicknesses.
The first set used the congress mash where you have a 1 C/min rise from 45 C to 70 C. At 70 C the mash is rested until fully converted. This is not a practical mash for brewing. It is a laboratory mash used for evaluating malt.
The 2nd set of experiments used the same mash profile with the exception of an added 30 min rest at 64 C. The experiments were done for mash thicknesses ranging from 2 l/kg to 5 l/kg (~1 – 2.5 qt/lb).
As you can see the addition of the 64 C (~147 F) rest was able to boost the attenuation limit in all cases, except for the very thick mash. The explanation given was that the thicker mashes are able to better protect the b-amylase with resulted in more fermentable wort for thick mashes in the 1st experiment.
A 30 min rest at 64 C was able to compensate for that and because of the aforementioned formation of dextrines from sugars, which seems to be greatly accelerated in thick mashes, the fermentability actually drops for the 2 l/kg mash when a rest at 64 C is added. It seems that these enzymes are most effective in thick mashes. This reminds me of the discussion whe had a while back when I found conflicting statements about how mash thickness affects fermentability. This data shines a little bit more light onto the subject and while it is not able to simplify the matter it can exlplain why the data on that seems so conflicting.
When I evaluated the effect of mash thickness on attenuation I used isothermal mashing (fancy word for single infusion) , which is different from these experiments, and was not able to detect a significant effect on attenuation. The same is true for the series with the 64 C rest which where you see a difference of 2% between the best and the worst.
BTW, the last row in the table shows the time in min that it took for the mash to fully convert once the 70 C rest was reached. It confirms my statements that tinner mashes tend to convert faster which can show itself as a boost in efficiency.