I can appreciate your comfort in using those boxy button shirts, but the reality of it is that I've known (and still know) guys who do the same, and while they think their waist-carried off-duty and retirement weapons are concealed, it's still easy to spot the bump under the shirt as they move, twist, bend and reach for things in their normal activities. Sometimes the consistent pattern of a design, like plaid, makes an unusual (even if momentary) lump more easily apparent to the eye. Draws attention to the discordant lines, so to speak. Especially if someone is looking for it and the nice lines of the pattern happen to drape over a curve. Of course, this is where untrained and inattentive eyes of nearby people may still benefit the wearer. Consider that some inconsistent patterns, like some floral print or non-uniform patterns (with irregular space between things making up the pattern images), may more easily draw the eye away from minor lumps or curves that don't have lines to make them more easily noticed. Nowadays some of the "deals" offered in lightweight "concealment" type short/sleeve shirts seem to be made using traditional plaid patterns, though. It's not always easy to find nice summer weight shirts that are boxy enough to loosely drape and that don't look like something from the 50's, or like someone's rendition of a bad print Hawaiian shirt ... or like they ought to be pajama tops. Having had to wear my fair share of boxy loosely fit shirts to act as cover garments over the years, I much prefer slightly more slimming shirts for normal wear nowadays. It's no doubt my background (martial artist, cop and firearms instructor) that influences me, but every time I see someone wearing an untucked boxy and loosely fit shirt, I check their posture and gait for signs of them wearing a belt gun (whether OWB or IWB) and look for the expected tenting of a gun butt as the shirt moves with and over them. Old habit. Many times what we think is adequate concealment is more the result of being lucky that others are often inattentive and inexperienced in seeing the signs.