There will not be any difference in the blower fan speed, because the fan motor is powered by the 12 volt battery.
There is a resistor in the circuit that will reduce the speed of the motor, giving you your different speeds.
The level of heat produced to the cabin is gained via the HV battery / inverter.
If the demand for heat is low, then it will be the same output in Eco driving mode or normal.
If however, you want MAX heat to the cabin, this can not be gained in Eco mode.
Eco mode ( by its very nature ) is trying to conserve your battery range.
The MAX heat setting is hungry on range, so it does not go hand in hand using MAX range and Eco mode at the same time.
It just defeats the object.
Using Eco mode will prevent full MAX heat from being piped to the cabin.