[Advaita-l] Sandhyavandana procedure doubt

[Abhishek Madhyastha]

Pranams,

My doubt is that is it mandatory for brahmins to wear a upper cloth,
i.e shalya during sandhyavana? I'm an udupi kota brahmin(smartha) and
i was taught to do it just in the dhoti (kacche panche to be precise)
and I've been doing so from many years but recently few relatives of
mine(not kota brahmins) told me that its absolutely mandatory to wear
a shalya. I've never seen any of my cousins wear it. Contrarily, those
relatives say they've never seen anyone do it without the shalya.
Could some learned member please clarify this for me and tell me on
what basis this is practiced? Sorry for asking an off topic question.