Juniper SRX PXE boot

I have an SRX which is working as a DHCP server for my user subnet. I want to send PXE requests from clients behind the firewall to the PXE server located in a different location in the network. What is the correct method to do this on the SRX?

Is it with the dhcp-attributes line?

set access address-assignment pool usr-pool family inet dhcp-attributes option 129 ip-address 1.1.1.1 

Has anybody got a working example of this?

I also see talk of a next-server

https://www.juniper.net/documentation/us/en/software/junos/dhcp/topics/ref/statement/next-server-edit-system.html

Is this required for PXE or not?

Thanks