The F/C key on most clarinets is almost always wildly under-vented. Common wisdom among many repair techs is to vent the F/C key so the pad is visually just above the body when viewed straight on. Of course, everyone accepts that each horn will require a slightly different set up once the play testing begins, so the height of the keys will vary somewhat, but generally speaking the pad is usually just above the body.
Look at the before and after here. When this horn came in, an SML Strasser, the owner said it played, "Pretty OK". And he was right, it was pretty ok. Not the best selling point. To be fair, there were other issues, like the knot-ridden cork pads on the upper joint, but that's another story.
The first picture is how it arrived, the key is vented .097". The second photo shows the set up when I was done with the Overhaul, it's now .157" That is a huge difference, and it is profoundly better.
To open the F key this much, the geometry of the F# key must first be altered, the F lever often needs to be cut, and then your adjustment materials need to be changed up. It's not like raising the height of the lower stack on a saxophone.
When I set this horn up I knew before the overhaul started that I would need to do this based on what you see in the first photo.
I adjusted the F# key, increasing the angle of both the key arm and the touch piece, did a preliminary check, and then backed off on it because I thought I went too far.
Two days later, when I got to play testing the horn, it was pretty underwhelming. Especially low G, it was as furry as could be.
So, I had to get back into it and increase things. I repeated the process until it finally responded with this beautiful, clear, uninterrupted tone that inspired me to make music with it. And that is what you see in the second photo.