I understand the basic principle of adjusted T-pace for JD: T-pace should be fairly comfortable for a 20min run, so if we do longer that 20mins of continuous T-pace running then the pace needs to be adjusted.
I also understand the basic principle of what JD calls "cruise intervals": we can do a, say, 5 x 5min T-pace w. 1 min rest session and run each of the 5min reps at unadjusted T-pace (even though we're running 25mins T-pace total) because the rests make the workout slightly easier on the body.
But what about longer cruise interval sessions like, say, 4 x 10min T-pace w. 2 min rest? There are several sessions like this in his Marathon Plan A. You're doing 40mins of T-pace running in a workout, so presumably you wouldn't want to aim to do them at unadjusted T-pace? On the other hand if you use the pace that you would for a continuous 40min run that makes 4 x 10min look relatively easy.