Dimentional errors can't be solved by sccaling - Any advice?

Hi there,
If got follwing issues: print quality is pretty good
But: there are dimentional errors that I don’t know how to solve.

  • Walls come out to thick and xy-dimentions are to small
  • z-axis is ok.
  • The Extruder is calibrated.
  • I measured the filament diameter and adjusted it in the slic3r (1.1.7) settings
  • The printhead moves easy and does not lose steps.

to get good results I have to reduce the flow to 74% in Repetier manual controll or in slic3r settings (–>prints are great)
further reduction and the perimeters start loosing their bonding
I am printing PLA 200°C, 30mm/s
Walls of that should be 1.1 mm come out 1.4 mm = to thick
setting slic3r advanced extrusion settings from 98% (perimeter), 102% (infill) generated 5 perimeters stated with 0.2mm in the G-Code…
resetting those to default created 3 perimeters of 0.35mm as stated in G-Code… Is there a bug in slic3r (Using Cura just made issues worse)
Outer xy-dimentions are to small (28,05 mm instead of 28.25 mm) inner dimentions are off even more (20.05 mm instead of 20.75).
Testpiece is circular. But in my opinion its diameter is to big to suffer immensly from filament drag…

These errors don’t matter when doing art but they matter a lot when doing prints to fit. And as some parts are to big and others to small this is not a thing of scaling or shrinkage.

for any advice, help or suggestons I would be quite glad
Cheers.