In my opinion, I think the amount of enemies is just fine, there's no need to reduce the amount to fight. Although sometimes, I feel that Krokotopia is too easy and there should be more enemies to fight.
Prepare an appropriate strategy for example buff and get rid of the minions then focus on the boss.
In addition to that, if you are still having trouble try these: Treasure cards for minions. Treasure card buffs. Do side quests to gain a level. Play around with the deck to see which one works best. (Good testing grounds would be a boss in wizard city)
Treasure cards for minions.