I went out to test Arcane Circle after a single job point into it.
However, I'm getting values even lower than the pitiful amount stated in the job point description. With Arcane circle (without feet), I'm getting ~15.5-15.7% damage reduction, instead of the expected 16%. Even if it's calculated in 1024ths, the damage reduction is still too low.
It's not consistent with damage taken stat being additive with it, instead of the arcane circle damage taken portion, either.