A company runs a centralized inspection VPC attached to a Transit Gateway. Firewall appliances are deployed behind a Gateway Load Balancer across two Availability Zones. Spoke VPCs send East-West traffic through the Transit Gateway to the inspection VPC for stateful inspection. Users report that some flows are intermittently dropped by the firewalls, which log 'asymmetric routing' errors. The Transit Gateway attachment to the inspection VPC spans both AZs. What should the network engineer do to ensure the firewalls receive both the forward and return traffic of a flow in the same AZ?