PCC Loadbalancing Between of Limited CAP connection and Unlimited Bandwith connection

Hello Sir,
i have two Internet connections and using PCC load balancing method, its working fine equally

i have two lines, 1st is 12Mb and Second is 38Mb.

now problem is 1st line of 12Mb is unlimited and second is limited like cap of 500GB,

now i want that all network first utilize 1st Connection of 12Mb , then if needed more Internet then add extra Mb from second connection of 38Mb.

like if all network using 10Mb then it only use 1st connection of 12Mb and if all network using 16Mb speed then 1st connection use all speed of 12Mb and remaining 4Mb from second connection of 38Mb.

Is it possible, if yes then please guide me

Code im using right now, its simple loadbalancing

/ip address
add address=192.168.0.1/24 network=192.168.0.0 broadcast=192.168.0.255 interface=Local
add address=192.168.2.2/24 network=192.168.2.0 broadcast=192.168.2.255 interface=WAN2
add address=192.168.40.2/24 network=192.168.40.0 broadcast=192.168.40.255 interface=WAN4
 
/ip dns set allow-remote-requests=yes cache-max-ttl=1w cache-size=50000KiB max-udp-packet-size=2048 servers=8.8.8.8
 
/ip firewall mangle
add chain=input in-interface=WAN2 action=mark-connection new-connection-mark=WAN2_conn
add chain=input in-interface=WAN4 action=mark-connection new-connection-mark=WAN4_conn
 
add chain=output connection-mark=WAN2_conn action=mark-routing new-routing-mark=to_WAN2
add chain=output connection-mark=WAN4_conn action=mark-routing new-routing-mark=to_WAN4
 
add chain=prerouting dst-address=192.168.2.0/24 action=accept in-interface=Local
add chain=prerouting dst-address=192.168.40.0/24 action=accept in-interface=Local
 
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=both-addresses-and-ports:2/0 action=mark-connection new-connection-mark=WAN2_conn passthrough=yes
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=both-addresses-and-ports:2/1 action=mark-connection new-connection-mark=WAN4_conn passthrough=yes
 
add chain=prerouting connection-mark=WAN2_conn in-interface=Local action=mark-routing new-routing-mark=to_WAN2
add chain=prerouting connection-mark=WAN4_conn in-interface=Local action=mark-routing new-routing-mark=to_WAN4
 
/ip route
add dst-address=0.0.0.0/0 gateway=192.168.2.1 routing-mark=to_WAN2 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=192.168.40.1 routing-mark=to_WAN4 check-gateway=ping
 
add dst-address=0.0.0.0/0 gateway=192.168.2.1 distance=1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=192.168.40.1 distance=2 check-gateway=ping
 
/ip firewall nat
add chain=srcnat out-interface=WAN2 action=masquerade
add chain=srcnat out-interface=WAN4 action=masquerade