So just want to confirm that even if the caster is in melee with the model they are making an attack against that model gets the benefit of being in melee. I know they didn't used to but in mkiv I haven't found anything stating that arcane attacks have the pistol advantage.
#Arcane Attack targeting model in melee
vagrant pecan
raw eagle
You are correct. Arcane attacks do not, by default, ignore the target in melee DEF bonus, because no core rules say they do.
paper sand
Nor are there (currently) any special rules or model advantages that allow ignoring it.
oblique flame
Witch Mark lets you ignore it!