The only flaw in the setup is only half the core is getting direct airflow, the rest is not.
The oil cooler works by "trapping" the relative airflow between the cores via the cooling fins and carrying away excess heat.
if the airflow is blocked then the core really cant do its job because the air cant carry the heat away.
Any cooling device needs to be mounted with direct or ducted airflow straight thru the core for maximum efficiency.