… sufficiently high traffic overall that your IPs are not obviously connected, yada yada, but especially with mobile providers sharing IPs between users, this might contribute to obfuscate this connection a little actually and make tracking even harder).
If you use a proxy, especially one that only you are using, you are having both streams come from the same public IP, and Signal might be able to track the connection easier. A worthwhile tradeoff if Signal is blocked, but generally…