My set up didn't change the tune at all but allowed the engine to run in any direction W/O any issues. The Yak cowl & Suk cowls are the worst for air currants from what I have read, But my extra sure needed one, ran fat as all get out in a K/E one way only and sometimes in midrange depending on what I was doing The bottle stopped all that nonsense.
From what I have read and experenced myself, the bottle with a slighty larger hole for the tygon tube has worked well for me. The diaphram does need a certain amout of air pressure to operate, all your doing with the box or bottle is limiting the drastic change from low to high to obtain a even pressure for a level constant flow of fuel.

I put my bottle in the fuse with the opening facing the rear of the plane, so it will block any wind coming in from forward movment and it must stop any turbulances also both the planes I have done this to runs super in any position.
A few guys are cutting the springs also to help pressure issues and adding velocity stacks for less puddleing. So far I have not needed either of those mods.
Good luck