[RedDevil]

Ah, the gap in the side of the bumper.
Well I notice these days that many new cars seem to have ridges, scoops or other intrusions in their side bumpers; as if they were deliberately placed there to block or disrupt air flow.
I believe that is intentional.

Now why would that be good?
The reason may be that by blocking the air flow they raise the pressure slightly. That will guide the air to move over rather than aside of the car. The aerodynamic properties of the roof are generally much better than the sides, so that lowers the resistance.
So the bumper edges need to be not areodynamically shaped to help lower air resistance.
Intuitively this feels bad, but I've looked it many times over and it just seems to be like that.
So maybe you are better off removing the tape there again?

OTOH, if you'd block the central part of the upper and lower grill you will see FE gains.
Be sure to measure air intake temp. The underhood temperature should not raise too much - frying your 12V battery harms it badly.
I ran a cheap in/out digital thermometer under the hood until I got my UltraGauge.