I’ve seen that tribes often are used for the lands name –

Vasconia for the Vascones,

[A]Media for the Medes –

Sannica for the Sanni?

does this hold true, and is it just for tribes who end in Latin “-I”? What about “Ae” or “A”?

I've also seen as with the Sinti of the Maeotian sea they've been called the "Siraces" - any tips there?