i couldnt yet make a rule for it, but often the toughness and softness between different buyins levels are not directly proportional with increase in value of a buyin, and sure as hell are not linear proportional
i found lot of games at 1.20 tougher than those at 5.50 for example
one simple explanation of this strange phenomena is that NOW in .....2012 almost .... hehe
more and more people employ correct money management strategy , so that even if i can beat the higher level , variance of the game and money management rules force me to play the lower ones.
it was a nice surprise for me though to find softer games at higher buyins