I see from comment below that simple e rather than esan is not wrong, but why the preference here for esan? What shift in meaning does it make?
I think esan is the emphatic form, used to stress (emphasize) the pronoun e. This is described well in the tips to the topic "feelings 2". So, perhaps, in the example here you've come back and found someone in your chair.
Would bha e etc be wrong?
I was marked wrong for bha e :-9