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qazaz,
a flugel has LESS overtones than a trumpet. Overtones are the mathematical multiples of the frequency that you are playing. Strong overtones make the sound more interesting (brilliant and with character) and less like a flute. All hardware has a basic sound. If that sound is in the middle of what you want to accomplish, then you have a great deal of flexibility. If your setup is too light or dark, you are limited to what you can realize.
If you are not happy with your sound, it can be you, the mouthpiece/trumpet combo or both. Most players do not know what they are getting into when buying a horn because they to not play test it in a large room with good acoustics. A music store or practice cabin will NOT tell you much of ANYTHING about an instrument or mouthpiece.
You are not producing more air than your piece can handle! You are wasting a lot of energy when playing by using brute force instead of sensibly. There are many players with this "air" obsession that is a misunderstanding, or distortion of the real truth! Back pressure often comes with a bad playing concept and often has NOTHING to do with the hardware. Changing your embouchure will not cure anything if your concept involves force. Playing intelligently generally solves most problems!

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Whenever I feel blue, I start breathing again.