I've pored over endless sites and books and haven't gotten a definitive answer to this one.
Clear gravel would seem to allow better drainage than with fines, which when solidly compacted can become nearly impermeable. Lots of instructions call for the base material by names that aren't used by any of my local materials suppliers and seem to have differing definitions depending on where you look. (Road base, compactable gravel, etc.)So if you can describe the actual product you think is proper, that would be great.
I've seen pictures that show clear materials and materials with fines, but no one with an engineering degree citing any kind of code spec that I could translate to my local supplier's terminology. They basically use size and clear or with fines (e.g., 5/8 with fines, 1-1/2 clear, etc.). They do not carry decomposed granite, which gets used and cited for a lot of purposes by Roger on TOH.
Definitely clear compacted gravel behind the wall for drainage there; just wondering if there's a right or wrong answer between clear and with fines for the base under the wall.