Sounds like you got it about right.The PW here has hoppers that are about as big as the smaller adults, and they're cheaper!
Early on, I gave Milton a mouse that was too big (before I found this site!)- he acted like Grampa after Thanksgiving day! He kind of turned on his side even... if he had pants, he'd have unbuttoned them... lol
Mine's about 2 1/2 feet long now, and about 2" thick. My understanding is that they get long, then plump out. I just saw a guy's tonight that's not much over a year and is really thick (and a little over 3'), so that's what we have to look forward to! I remember being excited about him crossing the 2' mark!
Have you seen any adults in person?