Question: Is the top pipe the inlet?
I'm not clear about the inlet pipe of the PCS3. Is it the top or bottom connection?
Coils are mostly filled from the bottom up. However, the PCS3 is designed for maximum heat transfer and best drainage by plumbing the inlet at the top and the outlet at the bottom.

The overall difference in heat transfer is not a significant factor once the system is operating for awhile. Therefore, if you have plumbed it with the inlet on the bottom, there is no need to worry about it unless you are looking for optimum heat transfer. This would be an issue only if the system doesn't perform as well as you want it to.