It's all over the place; social security contributions are not included in the scheme. For example:
“Impatriates” – 70%/90% Tax break to attract “human capital” to Italy – Italian Tax.
The exemption applies only to income taxes. It does not apply to statutory social security contributions (pension and healthcare) which will be calculated on 100% of salary.
Nor does the special regime provide any exemption from Italy’s foreign asset reporting requirements or reduction of wealth tax generally applicable to people who are tax resident in Italy for any year.
But yes, you're right, I didn't know there was a cap; the percentage is calculated only to the maximum of EUR 113,520 (
Italy - Individual - Other taxes.).
So, if you make 1M and live in Sicily you'd pay only around 30K a year of social security. And then income tax on 100K EUR, so effective tax would be less than 10%.