I know nothing about Sony cameras, sorry, but the following thought occurs ...
I wonder whether one of these settings is the stop range for the exposure bracketing function?
In which case, unless you actually engage bracketing, that adjustment will (apparently) do nothing (to single shots), whereas the other adjustment should have an immediate effect on the exposure of your shots.
If they both have an immediate effect, perhaps it's just two ways to access the same thing?
- and I'm feeding you red herring
Cheers,
Dave