exactly. if you do these right you'll be working the tranversus rather than rectus.
get the flexors out of the movement just like jehova said -tilt your hips- and to that i'd add contract your sphincter.
you also want to release air support so once you get to an L shape exhale so there's no air helping you.
doing these as static L hangs is incredibly effective. here's the breakdown:
-pelvic tilt/sphincter suck/inhale
-leg raise to 90 degress or higher
-blow out your air
most people can L-hang if they hold their breath, but not once they release that pressure. try doing reps of 10 second holds or maybe even 5 and work up to a minute total time. you'll get more out of doing 10 static reps than 100 leg raises.