A rule of thumb back in the day (don’t know if it still applies) was 1 real money player per 7 sign ups as a fair indication of a ‘performing’ casino or poker room.
In your case 40 in 677 is about half that – it’s somewhere around 1 in 16.
Nevertheless, the market has matured a great deal since that time so I wouldn’t be too upset with a 1 in 16 conversion.
I would run an A/B test with a different poker room to see what the difference is, though.