At gathering, outside leves, i believe the cap is around 330. You might receiving it gathering in grades 1~2 tiers higher than your "current grade".

They might be changing leves 07/21 so, after patch, you can expect getting much more sp/hit during leves ^^

Right now i just do leves and complete guild task as BTN, not grinding outside leves unless i'm in need of a certain item.