having grown a few crops of autoflowering plants,I will add that I found that the seem to do better when started in a deep pot like 12 in min. my first grow only gave me 7-8 in plants in small cups,next I went to big gulp cups & got a little bigger but never got plants over 14 inches till I started them in a 14 in deep pot. transplanting from small to large didnt do much good either. my guess is that they throw a taproot down and depending on how far down it goes,determines how big the plant will get. just a wild ass guess tho so dont take it as gospel.@ for what its worth,I tried 1 in a 5 gallon bucket & it didnt get any bigger than its sisters in 14 in pots.
btw all were from same seed crop of a LR2 daddy and a LR deisel mom -deisel is noted for being small for autoflower.