Here is yet another way to help improve your frame rigidity. I would suggest installing them for the Y then X axis supporting the middle 2020 beams. You can also run them along the bottom beams but currently doing so will block your USB port. I'm working on another strut to fix that.
I printed mine with an 0.8mm nozzle at 0.4mm layer height, 3 perimeters, 3 top, 3 bottom, 100% infill in PETG.