Oh that sneaky celosia!
I planted brain celosia several years ago. It self seeds and comes up every year. It has many different sizes and shapes from short to about six feet and brain shaped, fan shaped and pointy. Is there any way to control the shape and size? Does it have anything to do with soil, food, water, crowding or anything else? I look forward to hearing from you
If the plant is a hybrid, then the seedlings may not come true to the parent plant. It is usually a random chance when a plant self seeds. There is no way to control shape and size.