Raycast detects box collider, but not capsule collider

I've been trying to use recasts to help interpolate the path of my avatar along a round surface. What I'm doing is adding the input vector to my original position vector, then using Physics.Raycast downwards from there. My raycast detects a collision if the collider underneath is a box, but not if it's a capsule (which is what I need), no matter where I cast along the capsule surface.

     bool CanMove (Transform origin, ref Vector3 input){
         RaycastHit hit;
         Vector3 down = input - origin.up;
         Debug.DrawLine (input, down);
 
         if (Physics.Raycast (input, down, out hit)){
             input = origin.position + hit.point;
             Debug.Log ("Move");
             return true;
         }
         else{
             Debug.Log ("Don't move");
             input = origin.position;
             return false;
         }
     }