The reason we say flatter stomach is because it works the lower abdominals, know as the the transverse abdominals.
These exercises are great for targeting this area:
1. Series of 5
a. Single leg stretch
b. Frog
c. Scissors
d. Double straight leg – this one especially – even add weight between the feet
e. Criss cross
2. Corkscrew 1 and 2
3. Pendulum
4. Hip circles
5. Toe drives
6. Pelvic neutral exercises
a. toe taps
b. leg extensions
c. double leg bicycle
d. double toe taps
e. monkey feet
f. inseam circles
For more great ideas come to a Pilates is my Lifestyle class 🙂