Amy x Tails is a basic regular ship in any other series.

a self-insert underdog figure representing "you" with the idealized girlfriend figure you wish you had that'd be your very best friend and love you forever.

Like Deku and Ochaco.

But what this actually means is that the guy is a regular human person but the girl is a manic pixie dream girl. The girl is effectively a cartoon abstraction of an "ideal" girlfriend, i.e. a Minnie Mouse. Like any Anime Waifu inherently is at their core, from a "love interest" perspective. Just as Sonic is the ideal guy, Amy is the ideal girl. Which is why Amy is "Girl Sonic", this is what that archetype is inherently, which is why in a world where Sonic is our lead guy, Amy is simply his love interest, when in any other series, she would've been Tails' love interest.

Case in point: The manga, where Amy is the girlfriend of Nicky, who is basically a Tails type of character.

Cosmo in Sonic X is also the exact same height as Amy, and Zooey in Sonic Boom is also around that same height. Taller than Tails. This just further emphasizes that the idea of 'Amy Rose' herself is basically the template for what a love interest for Tails would look like. For a self-insert underdog character like Tails, what is likely the least common is for the love interest to just be his own female counterpart (i.e. Cream), because the inherent concept generally goes "pathetic loser getting with the most beautiful girl in the world" in some form. Of course, there's definitely exceptions to that.