Here is something I found just now. The original BioShock was designed as an XBox 360 game, and therefore, supporting 16:9 is a requirement. The HUD is optimized for 16:9, the cut-scenes are forced 16:9, the developers claimed it was designed for 16:9, etc. But is the baseline FOV actually 16:9? Note when I say "FOV," I actually mean the entire field of view - not just a value representing one of its angles.
Anyway, before the patch, "baseline" 16:9 looked like this:
And the "vert +" 4:3 looked like this:
Then they added a patch that disables the hor + lock. Now it is hor + instead, and looks like this:
Compare the old 4:3 and the new 4:3. They are the exact same thing! Clearly, despite all the evidence to the contrary, the baseline FOV is 4:3, and the game was originally programmed in a way so that 16:9 subtracts from the baseline. With the patch, it instead adds to the baseline.