I'm an idiot. I had the inversion node plugged into the bottom value of the Add node. facepalm After a few more false starts, like reverting my scene to make that fix after going way offroad with other experiments and typing "97" in instead of .97, I've finally got it working. Caustics still look weird but I'm pretty sure the height and width of my gobo have something to do with that. An easy fix is changing the shadow blur radius but I don't want to do that since .5 is accurate for sunlight. This seems to be such fiddly, variable stuff.