You are doing it right.
You only want to pull gasses thru the investment and allow normal air pressure on the cup.
Generally, you hit the vacuum after you pour metal into the cup… if you vacuum before pouring, you are simply pulling cold air into the mold cavity, cooling the surface of the mold and more likely to get a cold shut off in some detailed or thin area.
Ideally the mold should be pretty hot when pouring. Fresh from the burnout if possible.
The vacuum not only helps pull any entrapped air out thru the investment… more importantly is pulls out the gasses that come out of the metal as it cools, reducing or eliminating porosity in the metal surface.