Query phase behavior

Hi,
I have a doubt about the behavior of the Coordinating Node during the query phase: is there a specific criteria which leads it to choose between a primary or a replica of each shard?
Considering the following scenario:

HOST #0
Coordinating Node

HOST #1
P1
P4
R3

HOST #2
P2
R0
R1

HOST #3
P0
P3
R2
R4

What should be the reason to make him choose to query P4 instead of R4?
Thanks,

Loris

The mechanism to pick the shards is called Adaptive Replica Selection. See https://www.elastic.co/guide/en/elasticsearch/reference/7.4/search.html#search-adaptive-replica