You'll get soaked at Terrapin Point; the entrance is practically dry

Not even close.

The entrance to Goat Island is near the American Falls viewing area. You get a nice breeze and some light mist on a windy day. Terrapin Point sits right at the edge of the Horseshoe Falls. You are standing inside the mist plume. You will be drenched in seconds.

Exact difference? Impossible to give numbers because wind changes everything. But if the entrance is a 2 out of 10 on the wet scale, Terrapin Point is a 9. Bring a poncho for Terrapin. Leave it in the car for the entrance.