Delayed connection when traffic crosses router domains in F5 BIG-IP

In our setup, RD2 is configured with RD0 as its parent (it's using the default route domain of the partition), but RD2 also has a default route pointing to an external gateway (outside the F5).

Now I’m wondering:

Could it be that, because of this default route, the F5 is sending traffic out toward the external gateway instead of handling it internally between RD2 and RD0?

Here’s the traffic flow we’re seeing:

Client (192.168.142.4) → F5 RD2 (192.168.142.9) → CORE → FW → F5 VIP RD0 (192.168.158.79) → Pool Member (RD2 - 192.168.152.15) → F5 RD2 → FW → CORE → Client

But ideally, since the F5 handles both RD2 and RD0 internally, and the pool member is also in RD2, I would expect the connection to be routed entirely inside the F5, without leaving to the external network.

So my question is:

How can I make sure that traffic from RD2 to RD0 (and back) stays entirely within the F5 and doesn’t try to exit via the default route?

Would disabling Strict Isolation and using forwarding virtual servers in both directions solve this, or should we instead remove the default route in RD2 and define explicit internal routes for RD0 destinations?

Appreciate any advice — we’re trying to avoid traffic unnecessarily leaving the box just to re-enter.