hanoi flights in nov: can it go lower?

planning a trip to hanoi in november for 2pax

nagtingin na ako sa skycanner and google flights, these are the flight prices I saw, ranging from 18k-21k/pax RT

kala ko maaga na ako, pero late na pala ata ako magplan huhu, ang tataas compared sa ibang nagpunta ng hanoi ng 15-18k RT na for 2 pax

though, i did see november is a really good time for north vietnam (so is this maybe why?)

QUESTION: possible pa ba to bumaba for example: kung may seat sale before those dates?

kasi ang alam ko sa seat sale example: seat sale this 8.8 but flight dates are Jan-June 2026

and what's your general rule of thumb when planning an international trip? how many months in advance?

thank you po 🙏