Why on Earth can you not use smithing to improve Studded Imperial Armor? It offers no higher base armor rating thatn regular Light Imperial Armor, yet the latter can be improved.

Oversight?

I did try training the steel smithing perk. No luck there.

I have noticed the same.

Oh well, just use the other set? :/

Made the silly mistake of selling earlier sets I've acquired and now I'm stuck with the reward from joining the legion as my only current source of imperial light armor.

You have to get the studded version in order to get the heavy shield.