Most academic theories of coalition formation concentrate on the totality of coalition places, not individual ministries. They're not policy-sensitive, in other words. The one exception is Laver and Shepsle, who note that a government could refuse a particular ministry or set of ministries, even if it brought it more seats
“a social democratic party may prefer a minority Centre party administration to a coalition between the social democrats and a party of the far right, if the very disparate coalition were forecast to generate a lot of grief for the Social Democrats in policy terms”But this doesn't make sense here. Radicals like EU affairs - it allows them to circumvent illiberal Italian politics. So perhaps, like most academic theories of coalition formation, Italian parties aren't policy sensitive, but rather weight more 'prestigious' ministries more. That tends to make portfolio allocation a more difficult job, since people's evaluations of prestige are more widely shared than their interests in particular policy areas.