I have several kydex OWBs, including two Ravens (as shown above), an older Bravo Concealment, and even a Blade-Tec.
As far as t-shirt carry/concealment, honestly the most important part is actually the physical belt connection. Many of the kydex holsters have the dual loops on the back of the holster, that will result in a bit of a gap (as seen in the right hand pic above). I generally find that adding some
pancake style wings will bring the gun in far better, and add them to all the dedicated carry holsters I use.
And if you want to go an extra step, a bit of padding at the bottom does the same thing for an OWB that it does for AIWBs, in that it pushed the gun tighter into you than before.