Size estimated. (Guide page lists size as 10-11 mm, so I adjusted my initial estimate to concur with that.) There were several of these slender-bodied flies in the understory--perched on leaves. (Thanks for correction on ID--see comments.)

7/17/2013 update:
Aha! Looking further at this, it is a very good match for Dialysis rufithorax--wing venation looks correct, and the abdomen has prominent spots, not bands, as in fasciventris and elongata (just 3 spp. in East):


so I am moving it there.
Image updated 10/20/20 (larger).
Update 11/27/20. Image below shows a male:

My image must be a female.