From my experience (limited) with outdoor speaker installs on a porch and a deck:
1)
Definitely use eaves (or benches) to protect speakers from the sun and precip. (No air in CO = lots of UV
)
2)
If using the eaves, use your ~30 degrees both down and in angle idea.
Place the extended intersection of where the two speakers are pointing at the edge of the deck farthest from house, at about seated ear height on your permanent bench.
The two speakers will have different down angles due to different install heights.
This will provide as decent stereo coverage as possible over as large a part of the deck as possible.
If I had to do my own install over, I would buy "
dual voice stereo speakers" where each speaker has the entire stereo signal. Due to the generally large distances between speakers, this type actually provides better outdoor coverage and more flexible install options.
One example (Not recommending the brand, just first one I found on web)
Cheers,
XEagleDriver