Nice reference.
Damn it, Jon! And, right after lupulus had gotten us back on topic
My interpretation was that the effect was not small. Higher efficiency at lower pH is predicted by Künze (not as far as 4.5 though). If attenuation were similar it would have been 1.012. 5 gravity points is not minor. Really nice experiment. One of the best from the Bru team.
I like your point of view on this experiment and is something I did not consider (or know). I'm just starting into this literature but at 1000 pages it'll take me a while to get there. I'm still learning about barley varieties of various growing regions