OF, good explanation.
In a 225, there are protections built in such that, should for some reason you elect to fly it 3-axis, at 60(?) kts the IAS upper mode automatically kicks in and the ac becomes 4 axis coupled.
The 155B is the same, using 60 KIAS. The B1 refined it further to include rate of descent detection, so it may revert to 4-axis at higher speeds if required.