I've been thinking about this. I have a new Echo 24 and it has the 150mm x 30° stem. I can pedal up the front and get to hopping fairly easily, and I can get the front up to ride a wheelie (well, I wouldn't call it 'riding a wheelie' yet since I'm only good for a few feet to 10 feet), but trying to pull up the front for a bunny hop or for the beginning of the manual -- man, it feels like someone has a bungee cord holding down the front wheel! I wouldn't mind trying a shorter stem just to 'ease' this task for practice.. Sounds like it worked for you.
Thanks for the info.