Apple head or deer head
Two distinct head types in the same breed. Apple-head Chihuahuas (the breed-standard show type) have a rounded domed skull and a short muzzle. Deer-head Chihuahuas (taller, more elongated) carry a flatter skull and a longer muzzle that gives the face a more elegant profile. We read which you have from your photo. Both are breed-correct and both read distinctly in painted media.
Coat type and color
Smooth-coated Chihuahuas read as sharper graphic subjects — Pop Art handles them especially well. Long-coated Chihuahuas (with feathering on the ears, chest, and tail) suit Watercolor and the smaller Royalty formats. The breed comes in every color — fawn, black, chocolate, cream, merle, tricolor — each rendered as your dog's specific shade, not a fawn default.
Where the small gallantry lands
Knight was practically written for the small gallant subject — the breed's outsized bravery meets a portrait format built for noble bearing. Pop Art suits the graphic boldness the breed already carries. The smaller Pomeranian-adjacent treatments (the compact court-portrait styles) hold the proportions correctly. The breed never reads as small in its own portrait — only in scale to surroundings.