Tough question...so I'll take the easy (and Best) way out.
I think everybody should start at Squonk's suggested level. If that's lacking a bit...add more to your particular taste. The next time I make this recipe, I'm thinking
I may up the rice to around 3.4-3.5%. But that's just me.
When I belly up to a vendor for a real horchata, what I'm thinking I'm ordering is a cold sweet drink with a light flavor of cinnamon in the background. Rice would be providing primarily body and only faint flavor. Certainly not near the rice flavor level of say ...rice pudding.
Ron
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"The basis of art is change in the universe."- Matsuo Basho