Sounds like a good plan.
The inlet is reduced to speed up water velocity and to ensure that the block works well. Its called jet impingement and increse turbulance and makes it easyer for heat to transfur from the copper to the water.
Its like the differance between a 120mm fan flowing 80cfm and a 80mm fan flowing 80 cfm. If you put your hand in front of the 80 it will feel alot colder than if you put it on front of the 120mm.
