Definitely a person's body type is worth taking into consideration, I for instance can conceal carry a full sized 1911 in an owb holster. However, either carry method it's grip length that will print in my experience.
I went with "other" because I think, ultimately, the holster you use has a very big effect on how concealable a pistol is. I carry a full-size 1911 and have no difficulty concealing it. I use a Galco Concealable belt holster. I carried a Beretta 92FS in a similar holster for a while. I carry a Hi Power in a Kramer Vertical Scabbard sometimes, too. All of these will hold tight to the body (as long as you have a good belt) and an overshirt will cover them very well.
I also have a Safariland paddle holster that is thick and bulky, but easier to put on and take off, and prints horribly. When I wear that holster, everyone knows I'm carrying. The bulge on my side is HUGE.
If you wear a bulky, thick nylon holster OWB or a paddle holster, EVERYONE will know you're carrying a handgun. EVERYONE.
Proportionately, I think its width. Regardless of body type or holster, its easier to hide an extra .75" of length or grip than an extra .75" of width.
A longer grip can be hidden more effectively by changing carry position. Small of back or appendix comes to mind. Length isn't a big factor for IWB carry if you're willing to forego low rider jeans and a smedium t-shirt.
Width is more difficult to conceal, though, as regardless of where or how you carry there's going to be that bump. Where the thickness is matters, as well. A revolver with a pencil barrel may be thicker at the cylinder than a comparable S/A, but the barrel is thinner than a slide and will be easier to conceal over all as the thickest part is right at the belt.
Having a good full-size grip is a major factor in effective fire control (for me anyway). The larger the grip I can carry, the better my control. I don't care too much for the dangling pinky.
Had to think about this a bit. Going to go with length of the grip. If you carry IWB or OWB on the strong side a long grip will stick out and print in the back. The grip may also bang on the chair of dig into a car seat.
Thickness is also important as it directly affects the position of the gun on the belt. For example I carry a Glock (fairly thick) at the 4 o'clock position. It is too thick to ride further forward without bulging out. My 1911 can be moved forward without the bulge.