Hi @somethingnicer 
The nut does have to match your fretboard radius. You could try making one from a blank but there are some premade ones out there for Strat style 12″ radius. 
https://www.armstrongmusic.co.uk/products/pre-slotted-bone-nut-for-strat-or-tele-neck-flat-base-12-radius 
🎸🎶🙂🙏