I know this doesn't go along with the plan, but I thought it might be worth posting. I experimented with decreasing reps as needed to accomodate fatigue, starting at a high level and dropping reps off proportionally as needed.
No clear levels for D1 and D2
Difficult to tell which level to pick D3 from
Harder to gauge progress
Often, there's a "crash and burn" after doing the high level rounds, lowering workout density and thus compromising the training effect.
cumulative burnout may come faster if you push too hard at a level that is not appropriate for your fitness.
Good to aid transition between levels (helped me transition from L4 to L6)
Fun to see how many L8 D1 and D2 rounds I can get in before backing off.
If you check your ego at the door, this can be used as a bit of a break.
The thing to remember is to let your pullups be your guide and adjust everything accordingly.
D1 has a rep ratio of about: 1 pullup: 2 pushup: 3 squat
D2 has a rep ratio of about: 1 pullup: 3 pushup: 5 squat
So, say you start out on D1 and do 5 pullups/10 pushups/15 squats for five rounds before your pullups start to get ugly. On your next set, drop to 4 pullups/8 pushups/12 squats. As needed, drop to 3 pullups/6 pushups/9 squats (or 10 squats if you want to be right on the level), and if necessary, carry it further down. I try to make sure I get a round in at the start of each minute, so each workout done this way is by default 20 rounds for day 1.
Day 2 is a bit harder to use. Since the ratio is more heavily weighted toward pushups and squats, fatigue can still hit you hard, and adjusting the reps per round may wind you up with a less effective workout than if you just stayed at one level you could always get 5 rounds with. I guess that's another point against backing down. You could, though, just back down from L8 to L7, L6, L5, L4.
Beyond these, there is a question of whether this is an effective change of pace, or just using variety for its own sake. It has helped me, but I seem to thrive when I use a range of reps anyway.