Doesnt matter. Wound channel size increases whether its a solid or an expandable.
Without agreeing or disagreeing with the above, my point is that the reasons for wound channel size being a function of velocity are quite likely different depending on if the bullet is expanding or not.
Consider a non-expanding bullet at 1500 fps. Assume it has enough energy to create a pass through. Now consider the same bullet at 2000 fps. It too should pass through. If it creates a larger wound channel it will do so because of some phenomena based only on velocity.
Consider a expanding bullet at 1500 fps. Assume it expands. Now consider the same bullet at 2000 fps. Assume the bullet construction is such that the greater velocity causes it to expand to a larger diameter. It creates a larger wound channel due to the both greater diameter and (probably) velocity.
If you are going to get into a discussion about the OP's question, you are going to have to talk about how the bullet behaves.
