I would second Crothian's note.
In Kingmaker, your characters are exploring and settling a very large area.
The 'dungeons' such as they are, are fairly small, and you will otherwise be having outdoor encounters, or random encounters.
Because the encounters are built with the standard difficulty in mind, but you will not normally be encountering more than one or two at a time, players may feel very comfortable using most of their resources at the first sign of danger. It is meta-gaming, but it is also true. This is more dangerous on the random encounters, where you may encounter creatures severely more powerful than the party.
As such, if you do think your characters are having too easy a time in Kingmaker, it may warrant some GM modification.