- Mob's must be higher than lvl 50
- Mob must be check higher than "Too Weak" (Easy Pray and above is OK)
- The drop rate is the same across all mob types (there is no advantageous mob type to grant better drops)
- TH does NOT help drop rate.
- Drop rate is a static 20%
- It's a 50:50 chance to get either beastman seal or kindred seal (if you pass the 20% check on a > lvl 50 mob)
- All characters within the party are locked out for 5 mins before being eligible for another Beastman Seal/Kindred Seal to drop (multiple attempts at the 20% until 1 finally drops into the loot pool)

NOTE: you can't get seals from a mob that has mob modifier expressing the mob is to drop nothing.

There's a five minute lockout per seal per killer's party. If you're dual boxing set up an alliance and alternate which party lands the killing blow (or just don't party up). I don't think TH matters. On retail I experienced significantly higher drop rates killing shadow type mobs in fei yin. This may extend to fomor and kindred mobs as well. I do not know if that is emulated here or not.

I farm in Fei'Yin for Magic Pot Shards and belts and I get seals to drop like candy, so there may be some merit to your comment.