I second this post... I personally have exactly the same setup as you... A M&P Pro Series 9mm and .40 Shield... I live in FL and can wear cargo shorts and a t-shirt with no printing or issues. It is all about the holster. Crossbreed holsters are amazingly comfortable and are great for concealment. I also have nothing but positive to say about Remora holsters... Both have their distinct advantages. In most of my cargo shorts, the cargo pocket will fit my shield in a remora holster and it isn't as comfortable to me as IWB since it is an extra weight pulling on the bottom of your shorts but it is pretty much invisible.

As for IWB I wear mine around the 3.5/4 o'clock position and it sits there for 12+ hours and have no issues with movement or comfort with the remora holster. I am still waiting on my crossbreed holster to come in for my shield but I have a crossbreed for my FS 9mm and it was always super comfortable for the size of the gun.

Hope this gave you some insight!