FAMLI Leave True Up with PTO Hours

Anyone here used FAMLI benefits recently for bonding time? My employer offers a week of paternity leave and I was planning on taking advantage of Colorado's FAMLI leave to take another month off.

FAMLI leave only offers like 66% of my salary. I saw that you could "true up" your pay by supplementing it with PTO hours. How do I calculate that? I know you can't go over what your salary is, so I don't want to throw away hours by overclaiming. Are the PTO hours claimed based on my gross pay from my pay stub?