The tool change position must be set correctly for the simulation of 4th axis indexing parts to be accurate. Note that this does not affect the NC code, only the graphics.
The distance from the stock axis origin to the tool change point must be long enough so that the tool clears the part as it rotates. The figures below show the circle that would be formed by sweeping a tool change location around the stock axis. Notice that this circle clears the entire part.
See also Post options dialog box