WAN and failover dialup IPSec

Hi everyone,

I think I need some help. I will try to explain what I'm trying to achieve.

We have a headquarter and three small locations. In our headquarter we have a big FG1500 and on the three small locations we have FGT30E 3G/4G. The locations are connected through eternity circuit and and running OSPF between.

On the small locations I configured dial up IPsec through LTE to our main Fortigate with OSPF.

Everything is working fine on sub locations while connected to the ethernet circuit. I learn routes through OSPF as expected and can reach everything.... The default route is learnd from the headquarter Fortigate and that's fine....

When I disconnect the ethernet circuit the IPSec kicks in and the routes are learnd through the IPSec interface except the default route... Instead of learning my default route form the main Fortigate the default route from the LTE is injected in to the routing table with a distance of 10 I tried to change the distance under the LTE interface but then my IPSec goes down...

Someone any idea how I can fix that... What I'm trying to achieve is that the small Fortigate learns the same subnets and default gateway from the main Fortigate on the IPSec as when connected through ethernet circuit

Thanks