With the larger FMIC it will all the way around. Cooler operating temps from the intake, will also reduce overall heat and heat soak from the engine. Additionally, it's preferable to have the oil circulating thru the cooler at lower temps, which will also reduce IAT's, heat soak and boost performance especially in slower close proximity traffic. A cooler running engine produces more horsepower.Intercooler, sport-cat and flexpipe are the next parts to come
I don't think it makes any difference for track usage if the plate opens at 70 or at 90°C.
Once it's on temperature it stays open.
But for daily usage it's important. However for now my quick & dirty fix is duct tape on the front grill
If you really believe you have to; simply design and manufacture a pullover sock out of Gortex material, with a pull tie or elastic to cover the cooler. Sort of a small bag with a pull tie. This will still allow air to circulate but slows down the airflow thru the cooler itself.
Start out with something like this making it slide over the cooler. Remove the straps and add a pull tie or elastic to hold it securely on the oil cooler. Nothing fancy