The trick to IWB carry is to buy your pants with extra room in the waistband and hip area - "relaxed fit" works well for me - and to use the thinnest holster possible that will provide the needed rigidity for gun retention and reholstering.
I almost always use Kydex IWB holsters for that reason.
I find a leather IWB holster with a reinforcing band going around it to be way too thick. Soft, unmolded leather will not retain the gun without a retention strap.
Matt Del Fatti will make a leather IWB for my 1911, which, per his suggestion, will have reinforcement on one side only, with this side extending up under the thumb safety to hold it on safe. The reinforcement will be thin metal covered by thin leather. The other side will be unreinforced for thinness, and the molded leather should provide sufficient rigidity considering that the holster will rarely be empty when worn, and that 1-hand reholstering is not an absolute necessity for me.
None of this is R9 specific, but will work for any gun.
I have been very unimpressed with every tuckable holster I have ever seen (I've personally tried about 7). There is almost invariably some visible belt attachment, and tucking in the shirt makes the gun-shaped bulge very apparent.
