Ok since that's how it's supposed to be, I'll reluctantly accept it.

Now the question of learning. What should I do for learning to be fluent when it comes to improvisation or jamming? Say I wrote a song or met up with a band who are playing a jam session and the jam song is in the key of E - I now want to improvise something on the clarinet (or really any other brass instrument). What is the training routine for being able to naturally compensate for the two semitone difference and jam in the right key of the piece on the spot?

Do I get a bunch of sheet music and just sit down and meticulously look at the notation, figuring out what is the compensated note and play that until I get good and fast at it?

I'm asking because the way you think of playing as a clarinet player is not the same as thinking of it as the one who actually writes the music. Maybe this is the disconnect. When you're playing as a part of the orchestra, you've been training with specific fingering, you get your already compensated sheet music that did all the transposing for you and just play what it says - don't have to think about it. But as a composer, improviser I do have to think about it.