I don't know if this will help you any, but I have found that running a theater thru a HTPC pretty much eliminates this question altogether, as you can control the image size, aspect ratio, and a ton of other specs right in the software that you use for movie playback. In the literally hundreds of HT setups I have seen here on AVS, theaters that are HTPC based are(IMHO) hands down without a doubt, the most versatile, the most configurable, and are easily the simplest, to adjust and control. This of course depends on your specific situation and setup, but for the most part, that has been my observation.
As far as a practical, real-world example goes - consider these 2 different types of HT set-upsA)
Blu-ray player connected to a receiver connected to a pj. - all is on and running fine. On the wall.you see the splash screen for the BRP. You walk over, pop a disc in the player and sit down. The movie starts automatically, all looks and sounds fine and life is good. It ends, and you want to play another movie. You get up, eject the disc, hunt for the other disc, pop that new 1 in, and go sit down again. This time however, there's issues. The aspect ration is all wrong, the image spills off the screen and the sound is choppy. What do you do? Well, 1st you gotta look at the disc itself, then if that's ok, you gotta check wires for a bad/loose connection somewhere. If that all checks out, now you gotta start juggling settings and adjustments on THREE DIFFERENT UNITS ALL AT THE SAME TIME. Lets say after 20 min or so of messing about, you finally nail it. You finally get to watch the flick. You go sit down and enjoy the fruits of your labor. When that movie ends, for whatever reason, you decide you want to watch the 1st movie again, so, ONCE AGAIN...you get up, pop the 1st disc back in the player, sit back down, and now THAT movie is all screwed up on account of the changes you made to get the last movie to look right.
At this point, you just head into the den to find a good book to read for the rest of the night.LOL............................................................... -OR-B)
An HTPC with a (real or virtual) blu ray drive and playback software. The pc's vid card plugged straight into the pj, and the audio out on the pc's motherboard plugged straight into the receiver. All is on and running. On the wall, you have the computer desktop. Your theater is essentially a giant computer monitor right now. You load a bluray file into the playback software, sit back crank up the receiver(via remote of course), and enjoy the show. You next want to watch the same flick that gave the guy with Setup A(above) such a hard time, if for no other reason than to see what all the fuss was about LOL. You load the the bluray file for that movie into the playback software, hit play, and the movie has the same playback issues it did for the other guy. BUT! unlike your unlucky friend upstairs in example A, YOU were smart enough to have your theater based on an HTPC! So, WITHOUT EVEN GETTING UP FROM YOUR CHAIR/COUCH/BED/LIFEPOD/WHATEVER using your remote, you simply rt clk on the screen, make the 2-3 mouseclicks needed to bring the image inline - total of 30 seconds TOPS, and your back to watching this abysmal foreign horror flick, thinking it wasn't even worth the 3 clicks and 30 secs it took to make this dog bark in the 1st place LOL. At the end, you need to watch your 1st movie again, just to get the taste of that crap foreign film out of your head, so you reload the 1st file again, hit play and BAM movie runs perfectly, no readjustments needed, and the world is a right and happy place once again!
Now, it may seem petty to most - but the #1 thing about an HTPC based theater, -to me anyway- is that 90% of the time - assuming you bring your snacks in from the start LOL - is that you don't have to get up to adjust or fiddle with other components. Just sit back, and if you need to make a change or adjust something, a simple tap on the remote gets you back to the desktop and you make all your changes there. I have a digital collection of movies on it's own 8TB stack, and can watch anything from singing in the rain to avatar(yes in 3D) at basically the touch of a button. AND I can do the same with youtube, hulu, vimeo, and webpages, etc,etc,etc too! I can play a game(2d/3d) or watch cable tv(also 2d/3d). I can listen to an audio book or even an audio cd with the funky visualizations turned on and have my own midnight bakefest in my own private lazerium! - remember them from the 70's?! LOL Hell, I can even send a null signal to the projector and have my own bright white stage spotlight! Then I could get up and do a tap dance routine for my cats and it'd be like I was really on a broadway stage. If I had cats, that is. Or if I knew how to tap dance. You get my point tho.