Alb, with the tape you are effectively obscuring the upward flick of lighting on the left hand side of a UK car looking forward.
The upward flick is used in the UK to illuminate the pathway for pedestrians and other obstructions.
Line up the car if front of a wall or garage door, switch on the dipped headlamps
and look for the upward flick of light and then position a piece of card over the lit headlamp to give you an idea of where the tape needs to be positioned.
Failing that buy a set from Halfords, the sets contain a guide to where to position the tape.
