Mine is, the required one, a BC 3 pound, mounted under the sink, on the forward bulkhead, right inside the door. I have had 15, Vessel Safety Inspections, and only once was it mentioned that it was not in a convenient location.
I also carry a 5 pound CO2 extinguisher, just inside the companionway to the V-birth. That would be my first, go to device in case of fire. It is bigger and heavier so it is near the floor.
The CO2 is a much better FE device in that it does not do more damage that what the fire dies, and it does not require extensive cleanup of the somewhat caustic dry white powder.
A number of people (like me) mount them inside above the cabin main door.
It's out of the way, but also highly visible and unlikely to be stuck behind something.
Had to laugh at cbbernard's comment about banging his head on the door frame. I put foam padding on mine after I acquired several non-age-related creases in my forehead.
On the 25, there was a halon type right by the galley (outboard of the helm seat). A powder type under the galley, A powder type over the Port side window aft.
When stored upright the vibration and pounding on a boat can pack the powder in the bottom. It is advised to inspect and shake your extinguisher on a regular basis.