"(1:300 to 1:500)"

Yup, that's the neighborhood of what I was fooling with. I was expecting fog and uneven development, particularly since I was dealing with a horizontal negative developed emulsion side up, but I just didn't get any of that. The negs were extraordinarily clean. I was using FP4, not tri-x, though. I've got some of the Efke and J&C films on order to experiment with.