Let me just clarify that this is my guess of how the 18 day sched will shake out.
It is a educated guess. That is my thoughts on how it will shake out also, or something close maybe 6 on/3 off/6 on/5 off/6 on/4 or 5 off, depending on the month.
4 on 3 off, just isn't going to happen with any type of regularity.