think it depends on how u learn the gemara on 2b.
Similarly we say ain onshin min hadin- we dont learn out a punishment in bais din from a kal vchomer. According to the Maharsha this is because a worse crime may deserve a worse punishment. Being that the punishment’s purpose is for a kaporah, a worse crime may not be covered by (/deserving of) this kaporah and bais din wont be allowed to “help” him with the punishment of a lighter offense.