I have this same extruder on my Voxelab Aquila.
Default E-steps are 93. Using the printer menu to feed 100 mm of eSun black PETG filament I measured a feed length of 66 mm, so 34 mm under extruded.
Using the formula 100 / 66 * 93 gave me a new E-step value of 140.9.
Upon re-testing, I found I was now over extruding by 34mm.
This formula is missing something. ...