Not sure how to do this in Estlcam, maybe need to configure the bit as a large flat endmill matching your level/surfacing bit dimensions?
While following LR3’s docs for initial squaring, I stumbled onto @jamiek’s Surfacing gcode generator. Jamie wrote up great usage info. I just filled out some parameters, generated gcode and opened in Repetier, ran great (use 1" surfacing bit from amzn).
Short video clip, don’t blink… 19:16 Surfacing Spoilboard
Have used Fusion to create surfacing toolpath before. However, @jamiek’s script was way faster for me to generate and use.