[Multi-WAN] Routing of TCP-Reset packets (TCP packet with RST bit set)

[pfsenseddc]

Hi,
I have a problem, maybe it is because my pfSense configuration issue. But after two days of digging I suspect that it can be a FreeBSD feature/bug.

In a nutshell - I have two WAN gateways: WAN1 and WAN2, where WAN1 is set as a default one. I have a pf rule on WAN2 were action is set to 'reject' external packets reaching TCP port '21' (it is important that it isn't a 'block' rule action) .
A 'Reject' action should reply with TCP RST (TCP-Reset) packet and it take place but that packet is routed via WAN1 instead of WAN2, as it is to be expected.
Do you have any ideas how to force TCP RST reply via WAN2?

A configuration option at 'System:Advanced:Firewall/NAT->Disable reply-to' is not checked.

Thanks and regards,

–
John