But I've watched it a couple of times now and he definitely says that tubes down is optimal to get air to accumulate as far away from the tubes as possible for noise and longevity reasons but if that isn't possible and you have/want to front mount it for whatever reason, provided the pump (if it's in the block) is below to the top of the radiator you should be fine.
I'm confused about Alex's point at 1:25:53 about AIO placement. I remember there was a whole debacle about people not getting the point of Steve's video about it a while ago with people stating that you HAD to have your tubes at the bottom when front mounting. But I've watched it a couple of times now and he definitely says that tubes down is optimal to get air to accumulate as far away from the tubes as possible for noise and longevity reasons but if that isn't possible and you have/want to front mount it for whatever reason, provided the pump (if it's in the block) is below to the top of the radiator you should be fine.