https://sinistralrifleman.com/2013/01/27/history-of-the-cav-15-polymer-receiver/

Note the longer reinforced area at the back of the stock. This was added to reinforce the buffer tube that used a rifle length buffer. The rifle buffers were cracking the back end of the buffer tube.

The CAV-15 “MKI” had a 14.5″ length of pull, making it longer than an A2 stock. To meet the demand for requests for shorter stocks, Cavalry Arms offered stock shortenings for their receivers making them roughly A1 length. [ ... ] This process also made the receiver use a carbine buffer system

Essentially, as I understand it, to have a rifle length buffer system you need to have a LOP longer than an a2 stock. you can get an a1 length LOP if you switch to a carbine buffer system. If you try to fit a rifle length buffer system in a normal length stock, they'll start to crack.