How much of Italy could become Muslim?

Medieval Sicily was ruled by various Arab and Berber Emirs, but Muslim rule never spread further up the peninsula. Realistically, what is the best case scenario for Muslim kingdoms in Italy?, And what could be a plausible POD?
 
There's some evidence as it is that Muslims exercised varying degrees of control over parts of Calabria, depending on the year.

You'd need a more concerted effort to take Italy; perhaps a Rashidun/Umayyad-era spread that doesn't push into the Maghreb and instead goes across the pond. But that's harder to do since you need boats to ferry your army around. I may be wrong, but I'd think you'd have to do it before the Fatimids move their capital to Egypt; once they did that and took away the naval support out of Mahdia, probably the best you can do for Islam in Italy is surviving Kalbids of Sicily.
 
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