This problem can be caused by using the wrong inner diameter size. The bore size of the instrument should also be viewed with suspicion in these cases. As for flaws in playing technique, intonation problems set off the loudest alarms for me. For example, take the player whose pitch hangs increasingly sharper as he ascends in range. One probable cause for this defect is a mouthpiece cup that is too shallow.
Some players simply overcompensate by going into an overkill mode regarding cup depth.
The raised pitch indicates that he is really overpowering the capacity of the mouthpiece. On the other side of the coin, poor intonation throughout the range of the instrument often indicates that the cup of the mouthpiece is too deep. In this case the player is unable to sufficiently power the volume of the cup. Remember, the greater the volume, the more air required to maintain a constant velocity. In general terms, a heavier mouthpiece can work to darken the sound, add intensity to the core of the sound, and stabilize tone quality.