yes, there's a support layer between the big round hole and the hex but there is no layer between the hex and the upper filament hole which makes the ceiling of the hex drop down :)
i used a layer height of 0,25 with a 0,35 nozzle but tried to change layer heights to your settings - of course this didn't change anything - just tried. Am now trying a print with support and a 0,5 nozzle (0,30 layer height). But the support makes it a nogo i guess. You can't really clean out the
hex very good. I also tried importing the stl into sketchup to add another layer in there but this breaks the stl and netfabb isn't able to repair it.
Can you probably add your source file here or at least add another support layer "upstairs"? that would be awesome 8-)