All of my testing is done with a 1.4x8mm transponder, so if your using a 12mm one then you could potentially get slightly better results (maybe 1-2cm more) than what I will write about.
On the WL-134 RFID board we talked about above you need to design an antenna that has an inductance of around 600-620uH so will require an LCR meter to measure this.
You can use either a circular or rectangular antenna shape, use a calculator to get values on how to wind one to your specification from the link below.
Rectangular https://coil32.net/online-calculators/rectangular-multilayer-inductor-calculator.html or Circular https://coil32.net/online-calculators/multilayer-coil-calculator.html
My antenna was a square shape 200x200mm using 0.25mm copper wire with inductance value of 610uH at 7.7 ohms resistance. I have tried many other designs and copper wire thicknesses, but this one produced the best result for the physical dimensions.
To tune the antenna, remove all the solder bridge jumpers across J1 to J5. Place a multimeter into the circuit to measure the current drawn and measure the read range distance you get and write this down (current and range).
Then bridge J5 and repeat measurements (current and range). After measuring, remove J5 bridge and then bridge J4 and measure. Try out all bridges (J5 to J1) to see which bridge gives to the best read range.
I was able to get a read range of 12cm using this RFID module.
However I also contacted the RFID engineer of this board and they have a better version available here. https://aliexpress.com/item/32954572304.html
This module is much easier to use as it "auto tunes" the antenna so you don't have to mess around with soldering the J1 to J5 bridges. I call this module the AGV RFID Module.
For the AGV module you need to design your antenna using the calculators above to have a target inductance range of 100uH.
For my 200x200 square antenna the best combination I found was using 0.63mm copper wire with inductance of 107uH at 0.8 ohms resistance. This gave me 14cm read range.
As I spoke to the RFID engineer he said my results were very good, he has tried to design a module to get longer read range but the problem is very difficult and hasn't been able to achieve that yet. However the thing to remember is the 12-14cm read range is "good enough", you can indirectly get further read range by physically moving your antenna back from the point where your measuring from.
I would further note that you should do all your testing and measurement using a LiPO battery to avoid running into problems with crappy power supplies that will reduce your range or even prevent the RFID reader from working.
Use 7.4V LiPO for the WL-134 reader and 3.7V for the AGV.