What arguments don’t support the idea the two birth narratives can be harmonised?

Timescales: Matt 2.16 - the visit of the Magi in Bethlehem could have been up to 2 years after the birth of Jesus. In Luke the return to Nazareth from Bethlehem is little more than 40 days afterwards. Locations: Matthew: family home Bethlehem, journey to Egypt, settle in Nazareth; Luke: family home Nazareth, journey to Bethlehem (census), visit Jerusalem and then return to Nazareth. Characters: Matthew has Herod and the Magi; Luke has Elisabeth, Zechariah, shepherds, Simeon & Anna. Perspectives: Matthew focuses on Joseph, Luke on Mary