By code you should have your valves with anti-siphon above the height of your irrigation, or alternatively have a vacuum breaker before the valves. Depending on the layout and density of plantimgs, it may make as much sense to use continuous emitter line tubing at regular spacing acrosd the slope. I've used this approach with succulents on a much steeper slope, using 1/2" emitter line with emitters at 12" on center, laying out parallel lines at same elevation about 18" apart. Heavy mulch spread over all bare ground kept the weeds under control until the plants completely filled in in 6 months time. This system replaced an existing spray system which couldn't adequately soak the root zone without causing erosion and run-off. The water bill was halved, and pre-existing plants along with the new are thriving.

I've also redesigned steep slope plantings with existing spray irrigation which was not switched out with new supplemental plantings. Again, thorough weed control utilized heavy mulching to minimize weeds. This other garden slope was much more heavily shaded by trees, so water use is still reasonable given it isn't drip.

In any case, I'd recommend use of coarse fibrous redwood bark mulch to "stick" to the slope, and possibly clearing all weeds prior to applying mulch, and maybe applying a weed pre-emergent prior to mulching as well.