Hi James,
My 67cm Toyo Homer wouldn't clear a knobby 44, I don't think. With Dyad rims (18.6mm internal), I've run 43mm Gravel King SKs (not exactly knobby) and that was just fine, although it was admittedly very tight at the chainstays, and if I recall those tires were measuring in the neighbourhood of 41.??mm actual when mounted. When I was running wider rims (Crust, 23mm internal), 40mm was about the max in the rear, and even a 38 wasn't exactly swimming in mms of clearance. In the fork, a knobby 44 would probably clear (I ran the 43mm Gravel King SK on the Crust rim with no clearance concerns at all in the fork). FWIW, I think my next Homer tires will be 40mm Challenge Strada Bianca.
Mack in Alberta