Hi
I've never EPP'd anything with curves yet, so admire your bravery to try a clamshell! However from working with lots of curves when dressmaking, I'd say it will be very helpful to notch both the inner and outer curves.
On the inner - will allow the seam allowances to overlap each other for better fit, and conversely, on the outer will allow them to spread slightly.
I've only done hexagons so far, but for me regular printer paper is working just fine.