ILC and Tai Chi Principles

I've been wondering about the relationship between I Liq Chuan and traditional Tai Chi principles.  I am wondering if they are related, strongly related, or exactly one and the same.  I remember Michael Phillip's kai men exercises.  It seems the majority of them were aimed at opening up the ribs in every conceivable direction.  Having seen his form performed on Youtube, the quality of movement seems very serpentine, kind of elastic looking in a way.  There's a very obvious lag between when his hips turn, his chest turns, and his arms follow.  I understand this to be the way the Yang Tai Chi form is meant to be done.  In I Liq Chuan, we tuck the ribs, and it seems we move the torso more as a unit, with belly and breastbone staying in alignment as we turn side to side.  This is one example where I see what seems like a difference in principles of movement.  I would love to hear thoughts on this.  If there is no difference between the two sets of principles, It would be great to hear clarification on what the relavent movement principle(s) are and how they encompass these different outward manifestations.  Just an open question, inviting conversation.  I'll update here if I discover any answers to this on my own.