If you have the time, look closely at cable pulling tension calculations for previous cable pulls. Do you see anything in there regarding the raceway entrance? It's usually assumed that the entrance provides no additional friction. Typically, the reality is the additional friction can be significant enough to result in cable damage or an outright failure of the pull.
You probably inspect for any sharp edges in the pull path and remove them. You may even place a thick rag in front of the entrance. Those precautions are good, but you could still have excess friction. Some tips on eliminating it include:
At the pulling end, increase tension gradually. Jerking the cable can result in momentarily exceeding the calculated pull tension, thus dooming the pull to failure. Jerking is usually a response to an error at the feed end. These errors include things such as sharp edges at the entrance, poor lubrication, and spooling problems.