Hi Ram,
I used to believe in the Harington M concept until I was given alternative advice by a poker pro who had had this discussion with, of all people, Phil Helmuth.
So this is now my strategy based on those conversations:
7 - 11 BB shove with premium hands only, fold all others. Your personal range of premium hands would suffice here.
5 - 7 BB AI w any pair, any 2 broadway any suited connector 45, 56, 67 etc and any A. However.... if there has been a rasie in front of me and I have some information on the behaviour of the player, this may affect which cards to shove. If I am closer to the 7 BB than the 5BB I may just fold and wait. So you have to consider the dynamics.
=<4 BB - shovng ATC here really unless I am UTG whereas I will wait and shove on the BB regardless.
Of course you have to take into consideration certain environmental factors, such as are you short handed... your range can open up against 6 players as opposed to 9. Also are there antes etc.
I have found that changing from shove when your M <10 with ATC has been less successful for me.
It seems like the whole World understands Harringtons M concept so you get called with a wider range of hands.. You shove A4 and get called with A5 for example. So being more selective I find has led me to place better.