How small can the plants be?

[Fert1]

I've had pretty good luck setting out fairly small tomato plants as long as they're hardened off properly beforehand. Is that true for peppers though?

The reason I ask is that most of the pepper plants I set out this past weekend have died. I'm trying to figure out if they were just too small, too dry or what. The melon and cucumber plants I set out at the same time are doing quite fine.