I went harder on the first rep because I wanted to see if I could ride on the big ring ( but even without this I tend to go harder the first rep ), but thn I manage to stay consistently at threshold ( I find it easier to keep a steady pace when I’m more tired ).
I mean FTP.
I used to do a workout on a hard climb ( at least hard for me ) :
3x 7min all out ( no choice but to go full gas ) / 2-3 min rest ( basically going back at the base of the climb )
My FTP went up real fast the 2/3 month I was doing this, but I don’t think I would have been able to do this workout weekly for too long ( I was starting to build fatigue near the end of the 3 month )
Were you able to do all those VO2max / threshold workouts for a long duration ?
Now it’s 4th month. They are easier because they are not all out. The supra-threshold workouts in Sustained Power Build left me tired as hell. The threshold workouts are a lot more pleasant and I am able to recover a lot faster. During these 4 months I also build volume from LV (so around 300) to around 550TSS and now going gradually to over 600 TSS (this is my first year of riding a bike and training so it is probably the reason of the gains). The structure remains the same - 3 hard workouts (around 0.88-0.92 IF) and Z2 riding. The VO2 max block (3 vo2 max workouts day by day) left me tired with raging hormones 
but it is not an issue with threshold.
As I am coming to the limit of my time (around 8h per week) I have to start playing with stacking workouts and play with progressive overload little more.
I agree, I don’t think I could’ve done much higher. Did you do a block of 60 mins or split them into 2x 20s or 2x30mins???