NAT/masquerade not working on PPTP client when use-ip-firewall=yes

I seem to be having an issue with the interaction of these features. Basically I can see via torch/firewall logging that the packets are going out the PPTP client interface, however they are not being masqueraded as intended. If I disable use-ip-firewall, it works as expected, but as the cost of the marking/queueing.

Anyone have some tips? I’ve uploaded a diagram showing my setup.

Hardware: hAP/951Ui-2nD
Software: 6.34.6
hAP NAT flow - Page 1.png