Excellent point!! Even though you can technically track more because with the larger FOV you can anticipate more direction, if the subject movement is outside the DX frame you would lose focus tracking.
Thanks for making that point. One more thing to add to my new technique list!
Dan (Nikon D800,V2,Sony HX400V,Lumix ZS40) "I don't read, I just look at pictures" - Andy Warhol