Not sure what slicer you use, I only know Simplifed 3D 4.01.
For strong small parts, one would think more walls are better.. however, if you can have different settings for the pillars (S3d multiple processes) I would print 1mm below where they start up to the end of the print with 1 or 2 wall 100% infill. I am guessing as I would normally slice the part and look at the preview. Get your extrusion multiplier checked, print the entire part with NO FAN. PETG does not like fan.. Starting height has to be perfect if to close you will get Clingonbuggers that will cause issues, to high and no adhesion.
If you want to post the stl, I will load some PETG and print the part just for the fun of it. I don't like PETG that much but I do use it for part that will be in sunlight. My other go to is ABS which many people don't like but I have had a lot of good luck with, especially small parts.