Hmm, I thought in this case the Flip.fit() would use the stage at the time of the invocation within the timeline, which is after the 3D properties of the sliding image were set to 0. Sorry for the confusion, I'm still a newbie
The only reason I wanted to split the animation is that, with only using Flip.fit(), the sliding image turns inward pretty late and sort of look as if it's "free-falling". In the end, I modified the fit2D helper function, so that it returns a timeline.to() tween, which I'm calling after a tween where I'm rotating the image inwards and it now behaves the way I wanted it to
Thanks for all your help!