Looking at this, I would say you need to evaluate your rest, nutrition, hydration, and stress. If you have the data, look at what you did the day and morning before you rode FC. What was the last ride you did before FC? How did that go? Did you push it harder than necessary (bumping up past 100% or pushing it outside)? What have you been eating? Was it enough fuel for you? When did you eat that (too long before FC or too close to FC could have affected you)? Have you been getting enough water before ride? Have any adult beverages the night before? Has work been putting you under a lot of stress around those times you did FC? How was the family life?
I know you are not supposed to answer a question with a question, but I feel once you go through and answer some of these questions, you might have a better idea of what really was going on to drag you down or helping you feel great for FC #5. I don’t think it is possible to overdo you 4DP. You’re 4DP is your 4DP at that time. Sure, if you take an extended stay in Couchlandria after your test and jump back into FC, you are going to be in a lot of hurt. But, if you stayed on top of your training, you need to start looking at the whole picture and tweak what needs to be tweaked to help you get through the sessions. Also, I would shy away from adjusting the video off of 100%. Only time I’d move it is if I’m feeling really good and I know I can properly recover before the next ride (depending on the video/how I’m feeling, it’d be up to 105%), or if it’s just not my day (I follow this advice: Don’t Bail, Adjust Your Workout
I hope some of this could help you.