Greetings commanders,
as far as I can say is that there is a fixed value for the difference when the Morale malus starts to take effect. That value would be 4 for Morale Worlds and 6 for worlds having both, Morale and Forgotten Attacks. That is the only thing we can affect directly, the scaling of the actual malus is fixed however.
The scaling is however also affected by other factors like the Max level and world size, hence we resolved tho avoid launching Morale world with max level 80 for the foreseeable future. The increase in NPC levels is steeper on high level worlds, so the malus is more severe. We plan to have an update for the game in the future to enable more control for us to adjust the difference as well as the scaling factor manually for worlds.