Yes, I could see that. The air would float at the top of the lines or at the top of the radiator. I haven't had that issue at all, my AIO cools very very well. I'm really impressed with it, being it was like $150. I really wanna just build a loop for everything. I have a nice open spot for a water reservoir. I know if I did that, I could run my fans silent. Man, if you have a thick radiator, a couple or 3 fans at like 600 RPM will cool so well with a GPU or CPU vs a bunch of high revving fans. Water stuff is the only way to go.I read that there is a greater chance of getting air bubbles to the pump if the radiator is installed tubes up or if the pump is higher than the tubes at the radiator so i installed my tubes in the down orientation so any air in the radiator would be at the top away from the tubes.
My water pump usually at the highest is at 1200 RPM out of about 3600 RPM, while gaming. That's about 60 degrees C max, consistently (more like 57-58). It does the opposite of heat soak. I run the 4 fans on that CPU rad at like 950 RPM front and 750 back daily and like 1250 rpm front and 1000 back while gaming. The key is to have your fans just constantly pulling heat out of the radiator, so that way it literally never gets hot. The fluid is always the same temp so the AIO pump just has to spin up just 10% or so above minimum idle, about 850 RPM to about 1200. So playing my simulation game, my CPU will sit pretty steady from 56-58C, depends on room temp. I have my AIO curve set to spike up pretty hard after 65 C. Idk, I have so many fans lol, nothing gets hot unless I literally start turning fans off