Co2 guns. Does probe-size affect velocity?

[Goose]

The Beeman .22 QB78 has been modded with a probe from the original bolt-with-a-hole design.  Both to see if it would shoot a little harder and more accurately.  It was a "sput-gun" out of the box with velocities of a little over 400-fps.  Reaming the hole in the bolt to .105" helped some, but I decided that a probe might offer better performance all around.  That worked. 

The current probe is .100" in diameter (it's turned down from a motorcycle chain pin) and it works just fine with the (small engine fuel) hose as a seal.  But I have questions... 

Can velocity and economy be regulated by changing the diameter (volume) of the probe?  The aftermarket ones that I see all have a much smaller diameter, but I'm thinking that they're optimized for velocity.  Is that the case?  It seems to me that changing the volume of space between the pellet and gas source would affect the quantity and flow of gas.  Am I wrong?

TIA,

J~