Hi, sorry, haven't been on line much since the holidays began.
When I'm not sure of the amount sweet scenting advances, I just test the advancement. If you're on HGSS, find out the seed you're on using roamers or Elm calls. Make sure of which frame you are currently on, then use the seed in RNG Reporter to make a list of capture frames. Then sweet scent and look at the IVs of your catch. See how many frames you advanced and use that to adjust your Elm calls or radio advancements for your horsea catch.