Basically it isn't said but those 0.5-1PH could all be small workers hashing little shares with minimum difficulty while if you had 1 or a couple rigs that equated to that you "might" have a better chance.
Nope, it doesn't matter if you have one machine at 1PH or one thousand machines at 1TH each, a hash is a hash is a hash and any one has just as much chance of solving a block as another.