Yes you're right. The smaller 'n' is, the faster the speed of light in THAT medium.
In empty space vacuum, where the speed of light is fastest, n=1 exactly. In any material medium, 'n' is bigger than 1, and the bigger it is, the slower the speed of light in that medium.
The amount of refraction depends on the CHANGE of speed at the boundary. So when light goes from air or vacuum into, say, the 2.34, there's a big change of speed, and more refraction. But from space or air into 1.58, less change of speed, and less refraction.
If the light is going from a block of 1.58 into a block of 1.72, then not much refraction, because not much CHANGE in speed.
