Fixt! I switched out the emitters. On inspection, it appears to be installer error; looks like some careless person grabbed a few of the wrong emitters. Thankfully, I had more of the right ones. Does your porch look empty without your box of irrigation supplies?
Next project, electricity! This ugly-ass fixture has got to go. One flips the breaker first, though (carefully brushing the black widows out of the fuse box first)? I've spent so much more time with irrigation systems.