Is it possible to reduce range of an RF receiver or transmitter for LED Strip lights?
Rednecky Solution that worked:
Thanks for chiming in @mhaselup @Lundin @Bimperlrekkie @比尔盖子 @Russell McMahon @frr @Chris Stratton @Justin
For others looking for similar problem, here is what worked for me.
Issue: 3 LED Strip lights in different rooms, change together even if you want to control a single one.
Ideally, buy the IR lights, so you don't face this issue.
What did not work: Changes in Power Supply/Receiver did not work. Ignore my misdirection towards that plate and antenna.
What worked (takes 15 mins):

Open up the remote - Remove battery, Peel top layer and then open up 4 tiny screws. Pull the PCB out, gently.
Scrape off the printed connection to antenna, blue circle on right (or so I think)
I also removed a tiny component which appeared to be a resistor (left blue circle)
Put it back together. Insert battery
Had an adhesive backed foil laying around. Covered the led and some part of the back.
Done

Result = Distance between power-supply/receiver and remote now have to be 2-3 feet for it to work.