Overactive Illiopsoas/ Labral tears/ painful exercises

Hi there,
I was just curious, what is the reason why treatments involving hip extension is not appropriate for Hip labral tears?
I have a labral tear (well still awaiting MRI to definitively confirm) and an overactive Illiopsoas muscle which I need to stretch by completing illiopsoas release exercises from (starting position) crooked lying to (finishing position) supine position. If I try to increase the exercise and stretch the illiopsoas further by coming into a Thomas test type position/lunge it's incredibly painful. I guess what I dont' understand is why? Surely I'm just stretching out an overactive illiopsoas muscle? Why all the agony? Were it a tight hamstring muscle there would be no limits on how far forward to reach, I know not to do it (its hurt me and my patients alike) I guess I just need to know why? (and would like to know how I will know when I will be ready)
Thank you,