I have another alternative schedule. A few more rest days added.
Experimental Pattern - Two Title ZP Stack With Three Listening Days Per Week
Week One [Days 1 to 7]
Day 1: ZP Title #1 Loop, ZP Title #2 Loop
Day 2: Rest
Day 3: ZP Title #1 Loop, ZP Title #2 Loop
Day 4: Rest
Day 5: ZP Title #1 Loop, ZP Title #2 Loop
Day 6: Rest
Day 7: Rest
Week Two [Days 8 - 14]
Day 8: ZP Title #1 Loop, ZP Title #2 Loop
Day 9: Rest
Day 10: ZP Title #1 Loop, ZP Title #2 Loop
Day 11: Rest
Day 12: ZP Title #1 Loop, ZP Title #2 Loop
Day 13: Rest
Day 14: Rest
Week Three [Days 15 - 21]
Day 15: ZP Title #1 Loop, ZP Title #2 Loop
Day 16: Rest
Day 17: ZP Title #1 Loop, ZP Title #2 Loop
Day 18: Rest
Day 19: ZP Title #1 Loop, ZP Title #2 Loop
Day 20: Rest
Day 21: Rest
From this schedule you get 9 loops of each of the two ZP titles. The total number of loops in this 21 day cycle is 18. This alternative schedule is in between the listening guidelines and the recon reduction pattern schedule for the 2 ZP title stack.
As days 20 and 21 are rest days, maybe you could include those two days in the 5 day washout??? It would be days 20, 21, 22, 23, 24 as the washout days. If not, a full week washout in Days 20 to 26 is good too.