Gotta pay attention to the design of the inside of the catch can.
The oil mist has to cool, at least a bit, so it can condense more easily. Then it needs some kind of media to condense onto. Then it needs a reservoir to sit in where it won't get sucked up by the air flowing by.
e.g., I used a no-name can that just has a plate with holes bolted to a stand-off so it's sitting about mid-way in the can, and a sintered brass filter on one hole. I packed that area between that plate and the top with steel wool (check out any OEM breather - they're packed with a steel wool type material) and added some filtering material to the in/out ports.