I just discussed it with Kai over at the AIG discord and he confirmed that using reduced wingspan would need an adjusted AFCAD on some airports while others are fine out of the box. Bummer, but I am back to normal wingspan then, doubt that so many scenery designers are keen to offer two AFCADs for their sceneries...
EDIT: if of any relevance for you, Umberto, one of the cracks over at AIG added the following information I was not aware about: "Quick tip for airline codes, each airline position is also its priority for spawning in sim
For example: airlineCode"KAL,SHU,CES,SPA,EVA,CAL,CCA,TAX,HAL,THA,TWB,CRK,CQK,CQH,XAX,GCR,ABL,JJA,AAR,TGW,DKH,ASV,MXD,CSN,CSZ,OKA,CDG,FIN,CXA,CXA,CSC,TTW,SJX"
KAL=Priority 1
SHU=Priority 2
CES=Priority 3
SPA=Priority 4
EVA=Priority 5 and so on.
With that behaviour, every other airline will try to park before SJX. It's recommended that you at least randomize the order of every gate's airline code or find the specific spot for each airline as per real-world ops. When an airline is coded so far back, sometimes it will park itself in a remote stand or a gate that isn't coded at all"
Still does not explain why it goes total nuts when using the reduced wingspan, but then...