That's been my experience. The dwarfs bloomed at 6'-6.5' of p-stem and the orinocos at 8.5'-12' . The larger one leaned over and blocked my garage!
The yard from which these last ones were taken had some that were as you described, HUGE. There were many blooms on the property, some were on small plants while others were on mammoths. They all came from the same corm.
Here's the thread on it:
is this saba?
D.Orinoco (I think.....I'll know for sure as soon as it blooms) @ 6.5' :
(The inflorescense is directly over the radio)
Orinocos at 8.5'-9' :
I'm in Monroe.