When I first started making IWB holsters I thought heavy retention was really important. I went overboard because the cheap zero-retention holster with a metal clip I was using at the time made the gun feel very unstable and unsecure. Then I carried and trained with those high retention holsters I made and realized that when your pants are up into your armpits before your gun breaks loose of the holster, it's not very practical or efficient. Personally, I think if your gun stays in the holster when you hold it upside down, even if it feels a little loose, you're good to go. Your belt will increase the retention so it's possible to go overboard with the molding/boning, especially around the front of the trigger guard. I can't overstate the importance of practicing your presentation from an IWB holster to refine your retention (and keep your skills sharp). There are a lot of holsters that look fantastic but are not as functional as they need to be, especially in an emergency situation. Unfortunately, it a trial and error process. I've definately trashed a holster or two during the learning process.