Some filters are more specific regarding orientation than others. For example, the JetCat (aluminum) filter is advised to be mounted vertically to avoid air being trapped. The Intairco is more flexible, per the manufacturer it can be mounted horizontally or vertically. We just need to follow instructions... instead of tribal knowledge.

Also, as someone pointed out, it is true that some turbine manufacturers advise to filter before the pump, as debris can definitely harm the pump. But it seems we pretty much have consensus that we all typically filter our fuel before it enters the jet's fuel system. All good stuff, what ever makes you happy and feel better about your setup too.