NGINX SSL configuration

[henry_nginx_profile]

hello,i am come from china. i use NGINX in a short period of time. i have
some confuse about  NGINX's ssl_* directive.
i have two vhost conf file, the above is my configuration:

a.conf:

server {
     listen 443 ssl;
     server_name a.example.com;
     ssl_protocols  TLSv1.2;
     ...
}

b.conf {
     listen 443 ssl;
     server_name b.example.com;
     ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ...
}
my problem:
i test these two web site use curl tools, "a.example.com" is  using TLSv1.2
protocol, this is ok,  but when i testing  "b.example.com" that only support
TLS1.2 too,  it seems like b.conf 's ssl_protocols directive is not
effective, only a.conf's ssl_protools directive effective.

my question:
1.Dose ssl_protocols directive is only be parser once by NGINX? something
like NGINX read config file, that find out a.conf's ssl_protocols directive
and record it, the below ssl_protocol directive will be pass? 
2.if question 1 is yes,   how can i  write difference  ssl_*  directive in
multi vhost?

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,269177,269177#msg-269177