Conservative HU play in limit SnG
 

When i get to heads-up in a SnG, i find that i get much more conservative whenever a bet would put me under 50% or 25% of the chips. The theory being that if i have more than 50% of the chips, if i put my opponent All-in and i win the hand, i win the tourney. Similarly, if i go All-in with 25-50% of the chips and win, i get the chip lead. This seems like common sense to me.

I wonder how conservative i should be. I fold Qx in the Small Blind if calling or raising would put me past one of these thresholds. I think this is right, but i'd like to hear feedback from more experienced players, since i've been playing for less than two months. What about Kx or something like J9?