Hi until a VM business customer reply you can give some suggestions
For residentials as me we have the modem mode and is little more easy
But even we have not static ip, it does not change easy so in a way counts as static because i have done tests with the SH with mode mode and router mode
Here what you can try
connect the ethernet cable from the wan is nearest to coax cable to wan 4 of the draytek
Go to WAN >> Internet Access>>static or dynamic ip
ARP detect and set MTU 1500
Right page click obtain ip automatic (but field leave blank,router domain name)
click ok router will reboot so it should still connect to the VM servise so wait little time
Now go back to that page and should appeared (named) your ip, subnet and gateway
Now click Specify an IP address (which all info are there now) click ok to reboot and save changes
It always works for me but If still no subnet comes I also suggest if you have no modem mode maybe is better at SH to disable wireless (unless you need it) disable dhcp and vpn or maybe disable few other settings(to avoid confusion with the draytek)...
2 routers running together it will work but maybe is causing the issue so after disable them in SH try again
Hope this trick will help you if i understand well what is you looking for
