Thanks for the update Sam!
As for the question of why I chose 400. It was to get the cost of sending an NFT, FTs, or small payments down to about the same as a transaction fee.
This would allow people to send something worth $1 for a cost of about $0.20 instead of the current $0.70.
Choosing a value for the parameter in between the current and my suggested value needs to be low enough that the use cases are actually enabled.
Otherwise, there is no way to evaluate the success of the change.
Thanks for considering the proposal!