i think as i’ve dug two holes so far that one hole was sandy with clay, so that’ll be easier to penetrate through the other hole was pretty solid clay so i’d expect not much root penetration as i used that hole last year but a bit smaller and the plant was kinda short and narrow in height due to the hole size so this year i’ve doubled it in size..
so i don’t think it would get as big as growing in nicer soil in the ground.
many friends grew in their backyards in the ground, they say no clay at all and some plants where 10-15 ft tall..