Reed placement at the tiprail.
In the picture above, the rails on the left (A) are quite wide and on the right (B) are quite narrow.
The tiprail of (A) allows for several placements both further toward the top and further down while still holding a seal. The narrowness of (B) only allows for placement in the usual spot or further up.
- By placing the reed further up on the mouthpiece you are utilizing the harder, thicker regions of the reed. This will give you a slightly duller sound (not as buzzy).
- By placing the reed further down on the mouthpiece you are utilizing the thinner, more flexible regions of the reed. This will yield a buzzier, more responsive result.
By experimenting with reed placement it is possible to change tonal colors that may influence your feelings about your mouthpiece. If you have a reed/mouthpiece combination that is slightly buzzy and maybe closing up on you, try moving the reed a little up on the mouthpiece.
These are very slight variations. You can also experiment with reed strength as sometimes just taking your favorite Jazz mouthpiece and putting on a reed with, say - 1/2 more strength - can darken your tone enough to play the same mouthpiece in concert band situations. Again - YMMV (Your Mileage May Vary)
On some mouthpieces there will be some excess rail showing when you place your reed on the piece. You should still try to place the reed to match the tiprail and then straight down vertically with that.