A large throat will sharpen the upper register, and reduce the perceived resistance. This is true for mouthpieces designed around a large throat size, but not for drilling out a mouthpiece, which has the effect of enlarging the throat AND increasing the cylindrical length of the throat.
A longer cylindrical section in the throat will FLATTEN the upper register. It also increases the resistance and make it easier to slot notes.
A very tight throat will make the upper register go flat.
A tight backbore will decrease resonance in the upper register and cause it to go flat.
A very open backbore will favor the upper register, and cause it to go sharp.
This is why you hear trumpeters that either drill out their mouthpiece (increasing the cylindrical length) or use a mouthpiece with too tight a throat and backbore, in the search for an easy upper register, go FLAT when they are screaming.
The positives of a large throat are better projection and forte playing, and more confident pianissimo playing. But a tighter throat will help the upper register slot and resonate better. You can't have it all.
You need a good balance of design elements to make a good mouthpiece, and that includes the cup too. If you want a "bolero" mouthpiece, you probably want:
1. Low cup volume, favoring the upper register resonance
2. A tighter throat, increasing the resonance of the upper register, but at the expense of a flat upper register
3. A short throat length, which decreases resistance and causes the upper register to go sharp.
4. An open backbore, which is more open due to the short length of the throat. This increases resonance in the upper register and causes the upper register to go sharp.
Hopefully it all balances out, so that you get all that reinforcement to the upper partials, and the octaves are aligned correctly.
If you want a monster orchestra piece:
1. Medium to large cup volume, which darkens the sound and reinforces the mid to low range.
2. Large throat, medium length. Greatly increases projection. The large throat causes the upper register to go sharp, but it can be balanced out with the correct throat length.
3. A backbore that stays tighter closer to the throat and is not too open. This should balance out the rest of the intonation tendencies from the large throat.
Oh, and these tendencies will be different for different players. So it really is a crapshoot. The most popular stock pieces are just ones that are really balanced, so that they aren't immediately rejected by everyone as unplayable. You know, practice and all that
can cause injuries.
