Why write Eyvane no Eyvana?

Vowel harmony: a->a 

Dative: a/e

could you give all of sentence please? because, sometimes, there is no any rule for that. it depends on word´s root, i mean if it is foreing origin for example;

şahan-e (şah is from persian and means king)

and if the word came from ottoman turkish or it is foreing word or addition is foreign like persian addition or arabic addition, we do not look for wovel harmony.

Eyvane git.

Eyvan´e git.

With foreign places and names, you should go by the sound of the word rather than the spelling. So if the ´a´ in Eyvan sounds like an ´e´, then adding an ´e´ is more correct. I don´t think Eyvan´a git would be wrong.

Eyvan´e- My fault, sorry.

Anybody to explain me?