Like anything else, you've got to find what works best for you. Also, if your not willing to adapt somewhat to how your planning on carrying, its probably not going to work to well either.
If you "used to wear a 32 pant and wont admit to yourself your getting fat and really should be wearing a 36 now, trying to get that Smart Carry( or other types of holsters too, for that matter) to work under the 32's isnt going to work out to well. Different style pants or shorts can make a major difference in the way the holster works for you.
I normally wear "Carhartt" type work pants, which are basically full cut, but flat and fitted across the front. The Seecamp works fine with them, but my P230 wont. If I wear a pair of pleated dress pants, I can easily, and comfrtably get my P239 under them.
As with any holster, but especially with a new type, you have to experiment with how and what you wear. You may need to go up a size or two, or you may not. I normally wear my regular size pants, even with the Smart Carry and a P229 IWB. Its snug at first, but quickly feels right, and comfortable. Some cant or wont do that, but thats them, they have to do whats right for them, just like you do.
The problem with all this is, you have to buy the holsters and see how it goes. Thats why we all end up with a holster box. EBay is a big help in recovering some of that though. I made out great on the first box.