When I said don’t curl, I may have it wrong. I almost go out on a rant about this in https://mysterytomastery.com/topic/should-i-roll-the-lips-out-when-i-play/#post-39073.

I posted there the following:
What do you do to roll the lips out after “aah-ooh”? They are out. The only way I know to get further out is to pucker or pout with the bottom lip stuck out.

I know I have played pedal notes by sticking out my lips; but to me, there is a much better way. Maintaining your aah-ooh embouchure then relax corners, lower the jaw, and the tongue. I am able to slur from a pedal note to a non-pedal note such as C in the staff.