Between my career as a dancer, health reasons and menopause, my psoas has tighten up a lot. I have been doing a lot of work with constructive rest, exercises from Painfree by Paul Escoque and visualization while I move about my Iliospsoas. Another great resource about the psoas is The Psoas Book by Liz Koch and Pelvic Power by Eric Franklin.
I have come to realized that I am tightening my psoas while I am exercising. This is not functional, but a bad habit. I try to visualize the length of my psoas from the attachment to the lesser trocanter to the front of the lower thoracic spine. I work with imagery to feel the space of the illacus to soften and shape to the back of the pelvis. As I am able to connect to a new length and space of the iliospsoas, it is like a reflex for me that the abdominals hollow deeper.
Experiment with finding ways to release the psoas. Sometimes stretching it, tightens the psoas for me. Even training the psoas properly can get me to release the muscles better.