According to Palmer:
"Alpha amylase is instrumental in breaking up large amylopectins into smaller amylopectins and amyloses, creating more ends for beta amylase to work on."
So yea I would say in a given amount of time you probably get quicker conversion that way. I would guess that Alpha is still working even at 148, just slowly, for the well modified malts we use.
Happens all the time in my $hitty mash tun, probably done mashing in 30 minutes after I mash in for 10 minutes at 154 and I end up at about 148 for the other 50
I have a feeling that is why we homebrewers use more crystal than we really need if we had a proper insulating mash tun.