It's a lot of time, trial and error. That's why making them out of cardboard first is a good way to start. Attaching as much of one or the other baffle to the aircraft structure helps a lot with the cowl on/off sequence. It can all be quite a p.i.t.a., but sitting there looking at things for awhile often comes up with a workable solution. Being perfect is not a requirement, just getting close goes a long way to improving the cooling situation.