Great question and kudos for the observations you have made!
It's always a great idea to pay attention to what the very good players are doing.
Stack size varies depending on the structure but it is typically 10BBs at the last minute of registration for the regular MTTs on Chico. I will only last minute late register these ones if it is 8 max (not 6 max), as 10BBs 6 handed seems to be too little to work with. 10BBs 8 handed is fine, especially since Chico sits most late reggers together on their own table (this makes it easier to get away with pre flop steal attempts). I also will not register only 10BBs deep if a double up still leaves me outside of the money (for example 44 players are getting paid and I would need MORE THAN a double up to get into 44th place).
I also play a lot of rebuy/addon MTTs which I can last minute late register (right before the last rebuy/addon break) and get a full stack (rebuy immediately and addon) of 25BBs. These seem to be the highest ROI of any game I play (at least at the $1, $3, $4, and $5 levels).
Stack size is not really a consideration of mine normally, it's more that it plays a factor into my perceived ITM chances.
Every game I play, I take a look at the lobby and try to estimate my chances that I will cash. I have it to the point now in my memory, that I can quickly glance at the MTTs which are within the last 5 minutes of registration and determine if I should register or not. This is the critical aspect of the game that will improve your ROI drastically. Think about it: if you only register games that are easy to get ITM, you can simply get ITM first and then take your flips for building a stack.
With this being said, it's always a GREAT IDEA to work on your short stack game. Learn how you can work the small stack and linger around by timely small stabs or jamming in optimal spots.
OK, I hope this helps!
Edit: The answer to your question is that I last minute late register every game. Part of the math and why it works out is that I NEVER REENTER any MTT.