Hey OP,
Story time, grab a beer! I'll get one while I proofread this...
I agree with this. I've seen on another thread also that the temp of the grain stays in range. I haven't checked myself but considering the probe is on top of the element I'll take the word of the wise for it.
Other than what others have said, I can only ask/offer
the idea of vorlaufing before recirculating. Mine doesn't have that option so I wouldn't know, but my train of thought follows past experience.
I've had a stuck sparge with my vessel's bazooka tube from opening it all the way instead of a slow start.
Recirculating is essentially sparging on top of itself?.. maybe? Does the pump have a control valve or is it full on? Just an idea and if valid maybe it'll help you and others prevent a stuck recirculation.
As for your original question, I get 78%-83% efficiency. I do full volume mashes with a grain crush the size of a credit card. I seen that with it being so fine, conversion happens within 30min. (Don't take my word for anything, I'm just a non testing sheeple. although I do research a bit)
So I mash in with a stir to check for dough balls and pull the tube after 20min. I let it drain till good enough because it's basically my recirculation and let go to allow the slow sinking of this titanic. Try it, it's kind of romantic lol. I re-stir to break it back up and get it all rinsed/circulated then finish the 69min mash. (69min cause brewing is a good time
)
I was thinking that the tube water has all the starches/sugars and the "dunk sparge" mid mash would allow a good rinse. With all the starchy water now out of the tube (not quite all but goodnuff) which'll still convert to sugar and the grain has fresh water to release more sugary starch into.