Filament

The shape of an octagon give the ideal printing condition with 45° overhang and a good shape fit.

Layerheight

finer layer give a closer shape fit - else you need to add more flow when using, keep in mind that inclusive slicer setting will cause over sized filament.

When color mixing finer layer allow finer shade setting - while for dual color 0.2 is  fine (color change after layer 4) - print with 115% flow when using the printed filament.

Flow

Most default printer profile print with reduced flow - so measuring the octagon and check if you have 1.6mm over the sides. A perfect octagon would require 111% flow to match a ∅1.75 circle area. As layer will leave grooves you will need to compensate a little for that. Also depending if you slice exclusive, middle or inclusive (‼oversized) - the finer the layer the lower the deviance.