As those that know, every 5th tier of a stat = +1 of healing potency, enhancement potency, enfeebling potency, attack potency, etc. So, 5,10,15,20, etc. each would give one point.
However, when you're on BRD or ARC, it's every 4th. I just went form 255 to 275 PIE and got 5 Enfeebling magic. This doesn't occur on ANY other job, only BRD and ARC. I'm curious if it's a bug seeing as no other stat works in 4ths like this.