If its an ensete maurelli or ensete tandarra red (they have a reddish tint to there leaves), then they actually prefer partial shade to get the best color and healthiest growth. They dont like full shade, but also arent fans of full sun either. They also dont like drying out so if yours is that could also be a problem. My ensete has definitely grown faster and taller than any of my other banana plants this summer and it was in part shade but still saw lots of very warm direct sun.
Good luck!
-Alex

Hmmm...My ensete maurellis are in full sun and have grown HUGE this year...I used miracle grow during the growing season, but didn't fertilize as often as I should have...I got mine as plugs last summer ('09), they grew to be about 1' tall then and this year they were put in 14" square pots and are now 4' tall...We didn't have a super hot summer this year though.

Guess this doesn't help you much, sorry :(

knotz