How would you recommend to change the ratios if i'm doing this with an amontillado instead of a palo cortado ?

You're right, the syrup is a key component and a "sirop de batterie" is a must. However regarding the comparaison with the daiquiri the fact that there is no dilution and less lime (and juice+oil vs just juice) makes it a totally different beast even with the same ingredients !

Went with vanilla vodka and 1cl of passionfruit syrup (and no sugar syrup obviously), it was great !

The Medine distillery ans its blue penny range is also quite impressive and worth mentionning 😉