I don't think anyone else intends to, nor mentioned "sticking a fin" into CAS, which is obviously highly stupid because as well as being dangerous it will always be investigated in depth and the CAA do prosecute pilots for CAS infringements.
Perhaps you missed post #64, when Mar1234 said "
When the controlled airspace is 1000ft AGL, and I have little hope of a clearance, you can bet your last dollar I'm going to have my fin right up against the bottom of it. You might equally well ask why the professionals need fly so close to the base, and the wild, uncontrolled chaos that reigns beyond.."
The controller replied: "Not above 250 kts below FL100". I don't know if the other pilot was climbing or descending, or if he was inside or outside of CAS but that is irrelevant.
AGAIN, that controller wasn't speaking to an aircraft with a clean speed higher than 250 knots, was he?
He was not.
AGAIN, you're obsessed with the issue of speed here, when there are many aspects to the conversation, and the topic is mode C, not speed. You appear to have globbed onto one example, and appear to be unable to let it go.
Can we now get back to something more interesting and closer to the thread topic, please ... ?
Quite so.