Types of Bust, Head for Antoninianus (Roman Empire coins)

Hello

It would be very convenient for those looking to catalog their own currency or for those who want to add a card to have a link to the various types of busts and heads for the Antoninians.

For example here: https://en.numista.com/catalogue/pieces136409.html

I see Buste A, Tête K, Tête L. listed.

But there is no link to an outline explaining what they are.
And looking through the Numista documents I don't even find this scheme.

Thanks