I take it that most fresh air pulled into the case comes from the sides (which are well-perforated to allow this), and should then be exhausted out the top via AIO radiator?@smathev:
Is is not possible to install bottom fans on the A4-H2O.
On a sandwich style case like the A4-H2O there is no need for bottom fans. These fans would just add noise but no real benifit. Furthermore it would require much higher case feets of minimum 10-15mm to be effective at all.
Btw on the M5 you have to decide a thin AIO with thin FANs like in the T1 OR bottom fans. You cant install bottom fans + AIO.