You'll probably need to make the DHCP subnet primary, or use 802.1q and assign two VLANs, one for each subnet. This may be more scalable and flexible in the long run.
Think about it. Because no IP has been assigned yet, the DHCP frames have no subnet information. A DHCP request comes in on the interface but the primary IP has no addresses to hand out.
You would have the same situation if you had multiple secondary subnets each with DHCP. Which pool should be used for a MAC that doesn't yet know its subnet? Because of this ambiguity, DHCP to a secondary subnet will be problematic.
I would expand what jayh said but expand it some. Based on the config you are showing it looks like you are trying to run both internal and external network on the same interface, this is bad for many reasons and can lead to various network bottle necks, security, hairpins, and looping issues just to name a few. I would recommend that you use one port for your WAN facing port and the other port for you LAN facing port. If for some reason you can only have one port then you definitely need to go down the VLAN path, but if you have the equipment needed to run VLANs on your switches you should have the equipment needed to physically separate the ports. In your example you show your IP address of the WAN interface as being 220.127.116.11 since it is the first usable IP address in your block I am assuming your default gateway would be the last usable IP of the block in the ip route statement so adjust as need if needed. The below configs are estimated based on the provided simple diagram if your diagram is different please provide the diagram along with what you are trying to accomplish and I will try to assist you in a more specific manner. Hope it gives you some insights.
A simple diagram should be something like the following:
ISP Router--->924E Eth1 --- 924E Eth0--->LAN Switch
interface eth 0/1
ip address 18.104.22.168 255.255.255.248
ip access-policy Public
interface eth 0/0
ip address 192.168.6.1 255.255.255.0
ip access-policy Private
ip policy-class Private
allow list self self
allow list InterVLAN stateless
nat source list NAT interface eth 0/1 overload
ip policy-class Public
allow list Admin self
ip route 0.0.0.0 0.0.0.0 22.214.171.124
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