The HQ rate feels like it's different from what it says, but it would take a gigantic sample size to get an accurate reading.

For melding, the ~35% success rate on the first meld always seems to be closer to 50% for me; it seems like more than half succeed first attempt, the worst I've had is 6 tries, and at least 90% happen in first 3 tries (should be about 70% chance). The 2nd-4th overmeld have a much worse rate than listed from what I've seen.