Hi AkeFTH,
It sounds like you're doing route-based vpn on the SRX towards a Check Point firewall.
I will suggest looking at Traffic selectors where you define the proxy-id's in pair.
More information at this url: http://www.juniper.net/documentation/en_US/junos12.3x48/topics/concept/ipsec-vpn-traffic-selector-understanding.html