Are you referring to tucked under or kind of pulled up and under sharply as a first move? I learned something this weekend where you sharply pull the pelvis up, then drop the chest sharply and raise it back up sharply. I forgot what it was called.
on Saturday we were playing with oomis and playing with how to teach it and what muscles are you using anyway? and you tuck your pelvis under for doing that but it doesn't neccesarily stay tucked under because ofthe constant motion. did that make sense? does that count?
Basic posture with the pelvis is maintained through most of the fundamental families of movement. It's released when articulation with the pelvis is needed to initiate or complete a movement. Like pelvic drops, pelvic undulations, pelvic circles, pelvic figure eights. I tend to release it also with spins and traveling steps.
Yes, I keep my tummy tucked under when I shimmy. But when I layer the shimmies with undulations, fig 8s, hip cirlces, I contract and release as per the requirement.