Your super fast Sparge is the issue. With the Grainfather your efficiency is directly tied to this. The faster your sparge the less sugar you’ll extract from the grains. You could ask them to double mill maybe?
Grain bills high in Flaked adjuncts tend to Sparge really slow and you’ll get really high efficiency. I’ve never even had close to a stuck sparge with the Grainfather. You definitely don’t ever need to use rice hulls in my opinion even with up to 40% wheat I’ve had zero issues. Tons of Rye, no problem... lots of oats, no problem.
Yeah, that was my instinct - thanks for confirming my suspicions. Maybe I'll try a wit, heh, or bump up the oats in the next coffee stout: easier than arguing with the local shop. I have also half wondered about batch sparging by sticking the malt pipe in a bucket of water as a workaround.