Hey bud, I think you've just about got it - nice calling, man! A quick suggestion - try & make the purr just a tad bit softer. When you listen to a real hen, typically her purrs are much softer than her other calls.
Also, your purr sound you have is in the opposite direction - you're going "pppppUUUUURRRR pppUUUUURRRR" ; you kinda want it to be "PPPUuuuuuurrr PPPPPuuuurrrr"
Joe's video definitely rocks!