Just a comment though someone in the know could respond. Am playing game for first time live,via vassal,and am enjoying very much. After one particularly enjoyable reaction event play I discovered my overwhelming air and naal support did not gain a single bonus to my defenders in a ground combat. I saw rule afterwords but am mystified why an attacker can get +4 but the defender gets no bonus for this? Any ideas as to why my defense gets no bonus here? May be a question for designer, or perhaps it has been discussed before.
First you are playing the game correctly. EoTS handles logistics in an abstract, but historically restrictive manner. What is being simulated is only the offensive player has loaded in sufficient quantities of bombardment shells and bombs. The defender is opposing the assault with fighters (air to air) and ships (surface to surface/ air to surface) but does not have sufficient quantities of ground support munitions on hand for sustained support, which takes planning vice reaction. So, the defender can cancel the attackers bombardment and air support DRMS by contesting naval superiority and air superiority respectively.
I am glad you are having a good time playing the game.