This is not strictly an Arduino question, but maybe somebody here knows NFC well enough to help me out? Feel free to link a better forum if this is too off-topic.
For an art installation I detect NFC tags with a cell phone. Since the phone is hidden under a table, the reach has to be a few centimeters.
First I bought a few of these tags and the reach was about 30-40mm, which is good! Technical data: NXP NTAG 213, 13.56MHz, ISO 14 443-2 A, ISO 14 443-3 A, NFC-Forum Typ 2
Then I ordered 100 of these. They arrived today. The reach is under 20mm which is not enough. Technical data: NXP NTAG213 chips, Protocol: ISO 14443 A, Operating frequency: 13.56 MHz, Antenna size: 23mm / 0.91 Inches
Can you see the reason for the difference in reach from the technical data?
If not, is the reach defined in the standard so that I can claim better ones from the seller of my second purchase?
Update: Here's a video of me demonstrating the different reach. Turn on the sound to hear when the phone captures the tag.