为什么BouncyCastle会生成比.Net的ECDiffieHellmanCng更小的密钥

I'm trying to generate a public key with BouncyCastle (because I'm using Unity and do not have access to ECDiffieHellmanCng), and then I transfer the public key to the server which is using ECDiffieHellmanCng for its key handling. The server is rejecting my key, for what appears to be because of its small length. ECDiffieHellmanCng generates a public key that is much larger in size compared to that of what Bouncy castle generates. I'm trying to generate a public key with Bouncy