No I don't think you can do FIP by inning (open to correction). It is a measure of the season as a whole. But why would you need to because it encapsulates hr's, walks, strikeouts, innings pitched, and hit by pitch. The number is sound because it uses a fip constant to make it scale like era. Generally because his FIP is lower than his era it means his underlying performance is better than what his era shows. ie. maybe bad luck or bad defense, etc.