screamingmorris

I am just an amateur who played trumpet in Junior High, then I laid off trumpet for 30 years, then I returned to trumpet about 5 years ago.
So until last year I had never even heard of "slotting"
(and "water keys").

This morning I was using my Bach 7E piccolo mouthpiece on my .485 bore Conn 5A cornet (I *love* saying that because it sounds so strangely perverse, like putting a Bill Chase trumpet mouthpiece on a trombone) and I realized that until I was warmed up I could not easily lock onto any note above High C.
It was like trying to drive a car on wet ice.
After I got warmed up I was able to lock onto the notes up to High F pretty well.
Which led me to believe that it is my lips and not the cornet / mouthpiece which is doing most of the slotting above High C.

Question:
What is the main cause of the lack of instrument / mouthpiece slotting above High C?

The huge .485 bore of the Conn 5A cornet?
The fact that it is a conical-bore cornet rather than a cylindrical-bore trumpet?
The open backbore of the Bach 7E mouthpiece?
The combination of the Conn 5A bore with the Bach 7E backbore?
A characteristic of the Conn 5A that is unrelated to its .485 bore or conical bore?

I have read several times in the past that when playing trumpet *above* a High G (G above High C) or so most of the slotting comes from the player's embouchure control, because the notes are so close together in the instrument's falsetto range that the instrument itself cannot slot adequately in that range.
On the other hand, I have read numerous reports of people having to use alternate fingerings in the Double C range in order to get their trumpets to slot correctly.
Those 2 claims seem to contradict each other, yet both are common claims, so I don't know what to make of it.

But when using my Conn 5A cornet with a Bach 7E, it is as though I am hitting that no-slotting falsetto range a half octave lower, just above the High C.

If anyone can offer insights, it will be appreciated.

- Morris