Effective Embedment Depth

I have a circular arrangement of anchor bolts and I think I'm getting fairly odd results with the effective embedment depth. If I set my edge distance to 6" or more, it drastically reduces my effective embedment depth (I believe following ACI 318-14, Chapter 17.4.2.3, and taking the edge distance divided by 3). But if I keep my edge distance below 6", my effective embedment depth stays high, at roughly 11"-12", when my full embedment is set at 12". Why is my effective embedment depth being rewarded by decreasing my edge distance?