I've been driving diesels ever since I learned how to drive. I only made the mistake once re presuming the "reserve" capacity om the road and I don't want to make the same mistake again. [emoji3]
I always replenish the tank to full when it reaches a little bit over 1/4 but on out of town trips where fuel stations are farther apart, a fill up the tank whenever it reaches 1/2 just to be sure. Though the farthest I've driven non stop is 650 kilometers.
My mantra is to mix up fuel refills, sometimes half tank, sometimes more, sometimes less so the new fuel can mix with the old fuel already in the tank and stir up any existing "gunk" in the tank. This is regardless of it being diesel or unleaded fuel