radiator and intake hoses to allow tilt. Without this, the belhousing will be bumping into the bellhousing 'cover' - the body of the car. The spline on the shaft might also be interfering with the spline on the inlet and need a very small rotation. I usually get pretty frustrated at this point and start rocking the transmission up and down and rotationally.
Angle is the most important factor. Make sure the clutch tool has the clutch disk properly centered. If when lifting, you use a jackstand, you can actually un center the disk making it a huge pita..