Hi,
The interface's subnet and DHCP pool IP addresses should be in the same subnet. From the below KB article, it is mentioned that "Clients are assigned addresses from pools with subnets that match the interface on which the DHCPDISCOVER packet is received" - https://kb.juniper.net/InfoCenter/index?page=content&id=KB21909
You can also check the following forum link where another person confirmed that it won't work - https://forums.juniper.net/t5/SRX-Services-Gateway/SRX-DHCP-Server-not-distributing-different-subnets/m-p/479955#M57616