More info about bonus KD's Bonus Potions and Entrance Speed guide - #2 by Killerdog
Basically, the bonus will not increase by capturing monsters - otherwise it’s easy to get to full bonus by capturing multiple times.The bonus only increases when you get an extra copy of same monsters by hatching eggs using gems. The other way to increase bonus is to spend potions. If you are a new player, don’t bother too much about bonus now. Just know that many times you can get a copy of epic or super epic monsters which you already have through hatching eggs. For example, many times I get 0 new monsters even in 10 egg monster hatches since I already have most of epics and super epics in the game.