The reason for this as you might already know is that due to cam timing, intake runner length/dia, header length/dia, and all the other factors that affect cylinder filling, there is an increase of air and fuel being shoved into the cylinder. This is greatest at the point where torque is at its peak. Torque output peaks here cause the ramming affect of the inlet charge is, in essence, super charging itself. In some race engines like Nascar they achieve greater than 100% VE, with out turbos or blowers. This is due to intake and exhaust tracts tuned exactly and specifically to the cam, etc.

The air is drawn through the intake runners in chunks. The intake valve opens, the piston draws the air into the cylinder, air flow is speeding up, the intake valve closes, the air still has momentum and we all know air has weight/density, the air charge compresses behind the intake vale and surges back, much like a wave hitting a wall and coming back. Then it comes back again with almost the same force so as the intake valve opens the air is already moving toward the vale so the piston doesn't have to draw it in, it is quite literally shoving itself in the cylinder. The greater this ramming effect, the greater the VE.

OEM street engines usually don't exceed 85% VE. Hot street engines rarely don't exceed 90%-95% VE, full race engines are around 100%-110% VE.

In short, VE varies with RPM and is greatest at torque peak. Thus more air is being shoved into the cylinder so cylinder pressure is greater, therefore MORE TORQUE.

Now don't be confused, the compression "ratio" never changes, just cylinder pressure.