Those loaves are beautiful and yes, underproofed. So the dent not refilling is one part of the poke test. It is also the feel of the pressure/push back against your finger as you press down. You want a jet puff marshmallowy (not roasted marshmallow) kind of feel and development. This takes some experimentation to get dialed in. But you could have gone another 5-15 minutes on the proof, perhaps. The heat of your house will be a variable too.
The loaves do look really great and I understand your desire to perfect. You’re clearly on your way! Keep me posted.