Reinventing the wheel, yet again. The whole thing is 3 mm deep (z) and each strut is 1 mm wide and 0.8mm deep (so about four passes). The smaller one goes from 5mm to 50mm in 5mm interval; the bigger one goes to 75mm. Having trouble with my print bed so I haven't had a successful test yet, but pix to follow at some point.

UPDATE: Well, I finally figured out what was going on with my print bed and made some tweaks to the testers that helped. So now the testers have slightly rounded corners to ease travel jerk. They are 2mm deep and each strut is only 0.4mm deep, so each one gets 3-4 passes. But they print (see pic)! Astonished that my printer can bridge to 75mm if it wants to. So there we go. I'm not going to worry so much about infill anymore.