These two regimes of MHT can be understood in terms of the difference between the equator-to-pole imbalance of absorbed shortwave radiation (ASR*) and the equator-to-pole imbalance of outgoing longwave radiation (OLR*): MHT = ASR* - OLR*. In both regimes, the response is predominantly associated with the narrowing and weakening of the Hadley Cell with increasing rotation rate. In the slow-rotating regime, the narrowing and weakening Hadley cell reduces the heat transport by the mean meridional circulation; the resulting warming causes a local increase in OLR, which consequently increases OLR* and decreases MHT. In the fast-rotating regime the continued contraction of the Hadley Cell is also associated with a decrease in low-level tropical clouds, which increases the local ASR by an amount that almost exactly compensates the local increases in OLR. Thus ASR* - OLR* remains approximately constant, and therefore so too does MHT.
The behavior of MHT with $\Omega$ is consistent with the change of the dynamics with increasing $\Omega$. For the slow-rotating regime, the Hadley cell contributes significantly to the MHT. In this regime, the mass transport (and hence the heat transport) by the Hadley decreases with increasing $\Omega$, resulting in a decrease in MHT with increasing $\Omega$. In the fast-rotating regime, MHT is predominantly accomplished by atmospheric eddies. Consistent with previous studies, both the eddy length scale and the velocity scale are shown to decrease with increasing $\Omega$, rendering the eddy energy transport to be less efficient with increasing $\Omega$. However, the meridional gradient of moist static energy increases with increasing $\Omega$ -- mainly due to the increase in the gradient of moisture, rendering the MHT relatively unchanged in the fast-rotating regime.
We performed the same set of rotation rate experiments described above with three different estimates of (prescribed) ocean heat transport, aka Q-flux. The behavior of MHT with rotation rate is independent of the prescribed Q-flux.