Hi, there are some other factors to check.
1) The supply priority of the airfields where are stationed these bf109s. If you want them be replenished first you should put them to '4' (max priority).
2) the supply situation of the airfields where are based your airplanes. You need to have enough support squads, air support squads and supplies. Having supplies at Tunis port or depot it's not enough, you need them also at AFs.
Even with supplies situation optimal at AF in my experience I usually see some 3 new planes delivered to each group for each turn.
Edit: if you want your airgroups refilled quicker, you can withdraw them to a big depot AF in sicily for a turn or two.
Yeah, the systems works pretty strange.. my logistics situation is stable, the aircraft started to get replacements a couple of turns ago, but it still isn't enough, would be great to understand how it works, because now it seems rather random.