OH Breeder...I am thinking they are asking what you are asking, just maybe didnt know how to word it.
Its not really particular to shorthorns, most types of cattle are the same here. If you feed a high protein, low fat diet, then often times you will see cattle shoot straight up. Then instead of looking full and bloomy for the showring they look tall, shallow bodied and lanky. Like you said a good 12% Protein and about 3% fat diet should coast most steers along without them getting to framy and keep them looking full at the same time. However, if I have a steer that I still think is going to be to framy then I will up the fat content, generally by adding a fat supplement early on. I dont think it really stunts them, over time they will still generally reach the same size that they would on any ration. I just find that the higher fat content tends to slow down the fram growth a little so keeps them where they need to be in the showring without being all legs. At the same time, if I have one that I think may be a little later matureing frame wise and worry about him being a little on the small frame size, then I will sometimes turn them loose on a higher protein lower fat diet early on to see if I can get some extra frame growth out of them.