Question NHDA5S FRONT FAN REPLACEMENT

why wouldn't you be able to install a 120mm fan where there is a proper place for a 120mm fan?

if there is some issue that you believe may be preventing you from doing this
you will have to include more information.
Thank you for your response I really appreciate it.
the main thing is the NHD15S are coming with single 140mm fan, and i already don't want to spend more money to get another Noctua fan, i already have the silent wing 3 from be quiet but i am not sure if i can install it with Noctua as a second fan (front mount) due to any mounting incompatibly.