ssl-enum-ciphers script reports dhparam size divided by 8, that is when we generate 4096 dhparam with
openssl dhparam -out dhparam.pem 4096 ssl-enum-ciphers reports it as (dh 512).
openssl dhparam -out dhparam.pem 4096
Tested on nmap 6.49SVN (commit df5d9a7).
Thanks for the report. This was due to some confusion between DH and ECDH strength-vs-length equivalences. I have corrected this in ddc5762, with help from Brandon Paulsen.