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You're talking about a shirt-tucker holster, but you sound very concerned about definable bulge.

A good friend of mind makes a distinction between 'concealed carry' and 'covert carry'.

I'd describe concealed carry as 'reasonable efforts not to allow direct vision of the weapon'. To me, 'covert carry' is hiding the gun so well that just looking isn't going to detect it.

If you're carrying merely concealed but wish you were carrying covert, your anxious behavior may draw enough attention to 'make' you.

This sounds like a situation that's crossing from 'concealed carry' over to 'covert carry'. You might want to consider carrying in a way other than IWB. Pocket holster, belly band? (Smart Carry, Thunderwear?)

DeSantis makes a popular and inexpensive pocket holster called the 'Nemesis'. When I'm not using IWB, I like my Nemesis. :-) Hey, just noticed they've updated it, I may have to get the newer model.
http://www.desantisholster.com/n38.html
http://www.desantisholster.com/m44.html

You lose some speed and a lot of access, and gain concealement. If I buy another, I'll give these folks a hard look, too:
http://pcsholsters.com/pocket_holsters.html

If you have your heart set on IWB, I recommend Blade Tech. Their customer service is _outstanding_. Here's a Blade Tech tuckable IWB:
http://www.blade-tech.com/product.php?p ... 260&page=1
I have one, and find it very comfortable, though I admit I don't use the tuck often. I prefer the loose shirttail or an open over-shirt or jacket for my cover garment.

I recommend giving SideArmor a miss; I wasn't impressed with their product or their service. You'll find a lot of fans of theirs on GlockTalk, where they post and advertise.

Good luck.