Heatsink case: thermal pad question

My case arrived today and I started to assemble it, but there is an additional very small thermal pad in the box not mentioned in the yarr-niversity instructions. where does it go?

What model Pi are you using?

Its mentioned here, if this is the case you have.
https://learn.pimoroni.com/tutorial/sandyj/assembling-the-heatsink-case

using with raspberry pi 4, 4gb with the heatsink case
https://learn.pimoroni.com/tutorial/sandyj/assembling-the-heatsink-case

the how-to mentions what to do with the 2 larger thermal pads, not the small – trying to learn what the small pad is for.
https://learn.pimoroni.com/tutorial/sandyj/assembling-the-heatsink-case