sounds like you're messing about too much.

You NEED TO MEASURE the unsmushed diameter of the extruded filament - NOT guess it.

The reason for this is simple - the extruded width of the filament is the measurement that EVERY other calculation is based on.
Get it accurate and everything else works better.
Extrusion - I've always had it at 100% - but I measure my extruded filament :-)

What filament are you using and what temp are you extruding at - also what speed are you extruding at.
Temp and speed have a greater effect than extrusion %

The thing is, every make of filament has a sweet spot where temp and print speed meet and have sex and give birth to lovely printed children.

So it's easier to measure your extruded filament, set extrusion to 100% and adjust flow with temp and print speed.

The slicer is working off the right calculations so extruding the right amount of plastic. get the flow rate right and everything else should fall into place.