They are most definately two different things.
Volume is the amount of oil that is pumped
Pressure is the PSI of the oil that is being pumped
Below shows where the flash was on the BBC it didn't take much to remove it, you can also smooth out the rough casting in the lifter valley. to give the oil a smooth path back to the pan...some people even coat it.
There are also places in the head that you can do, the holes where you can see down into the lifter valley usually can be opened a bit.