I agree with your point about the boosted CHO not being necessarily as helpful, being that there will be no drop in T3 (being that this is in play exogenously).
That being said, I will personally only use/recommend higher kcals levels during a CHO-up on myself or others under three main circumstances:
- My/their appetite has gone, along with a higher than normal loss in fullness, and a loss of energy. A CHO up with high kcals always seems to bring myself, and some others, back to "baseline".
- Psychologically, I/they NEED a refeed.
- Progress has slowed unexpectedly.
Otherwise, I use CHO-ups similar to Erik Minor's suggestions, being that I will eat CHO and protein within my normal caloric allotment for the day.
Of course, I assume everyone uses different tricks to determine when CHO-ups are appropriate.