A reasonable 3D sound set of commands should include both range and volume which should solve the problem here.
In such small levels as FPSC using in particular an environmental ambient sound means it is quite likely that if you want a realtive high volume of sound at its centre radius then in an FPSC level you may well be able to hear it from one end of a level to another. Its an holistic background sound by defination and FPSC is designed by and large to play a single one for the entire level, well whole game really.
I use an entity to play 3D environmental sounds - so you could have more than one in differing areas of a level though you can see that this has implications for the mem consumption apart from anything else.
You may be able to switch an entity and its sound off and on by player proximity commands - I have not tried it though so it may not work.