Depth of seedlings

I'm growing a lot of new veg this year and raising a fair few indoors before planting out. Because of holidays getting in the way, I'm going to have to plant out earlier than anticipated. In any case, is there a rule of thumb for planting depth of seedlings started in pots? My cabbage for instance seem a bit on the leggy side despite being in the sun indoors. I'm tempted to put them in the ground gently burying half of the current stemp length to make them more sturdy in the ground. Will this be ok? And will this work for other veg? I know with peppers, chillies and tomatoes it is ok, but not sure with other veg.

Cheers
GG

 

Thanks JWK, I'll plant them a bit deeper then. By indoors I meant in an unheated garden room so much the same conditions as a greenhouse. All other seedlings seem to be stout and hardy even other cabbage varieties, just this one, Tundra is leggy. Anyway, I'll take your planting out advice.
GG