Problem with top layer

Hi guys, I own a prusa mendel i2.
have to say it is printing quite nicely but have tried to make bridging work and was unsucessful.
I also tied to print a wing for the 350mm glider and had problems with top layer.

Print parameters:
Nozle dia = 0.35mm
Fillament = 3mm
Hotend temp = 170
Bed temp = 50
Layer height = 0.1mm
Botom solid layers = 2
Top solid layers = 3
Perimeters min = 2
Fill density = 0.25
Fill pattern = rectlinear
Top/bottom pattern = concentric

Speeds:
Perimeters = 15mm/s
Small/Ext perimeters = 10mm/s
Infill = 20mm/s
Solid infill = 20mm/s
Top solid infill = 15mm/s

What happens is that the top layer does not cover the infill, so I end up with small holes in the top layer.
I use a 60mm fan with a custom fan mount blowing onto the print and hot end.
Here is a picture of the wing and I colored the spot around the holes.
I also use the latest wersion of slic3r with the detect bridging function so the fan is at 100% when covering the top.





Any ideas what to change or what im doing wrong?