Can anyone make a case for having the first layer speed only as a percentage of default-, brim-, perimeter- or any other speed for that matter? I can’t see a reason personally but maybe I am missing something.
A build surface with a specific temperature and specific adhesion enhancer requires a fixed speed for optimum adhesion. First layer speed should not be realtive to whatever speed the following layers are printed at. Bed adhesion properties doesn’t magically improve when the default speed of an object is increased.
First layer adhesion is probably the most critical part of a print and adhesion properties are (should be) static if the physical conditions remain the same between prints (temperature, filament…).
KISSlicer want a fixed value. Slic3r accept both relative and fixed.
I am trying to bring the issue to the attention of the #Simplify3D developers since the slicer require a relative value.