5600HSD Underexpose at tele?

[capedeci]

Im using the Kit Lens, at 70mm f/5.6, the flash (bounced) tends to underexpose. While it's perfectly exposed at 18mm. It underexposes at 70mm with around 2m subject distance (closup portrait).

It only properly exposed when I use +1 FEC. While in wide angle, 0 FEC did the job well.

Any thoughts?
Thanks

[Robert Besen]

Maybe your bounced flash is missing the target. Try changing the angle of the flash head, or the subject position, or take the flash off the camera to try other placements.