I think this could have been obtained with the older system if you used a different key type.

I think different keys yield different PGP signature sizes? for example this is “Hello! This Tweet has been signed with my PGP Key.” signed with an EdDSA 256 key (https://fozzie.dev/.well-known/pgp-key.txt) which gives a 326 character result: https://pastebin.com/izcEK4k0