2m USB-C to Lightning Cable charging iPhone more slowly than 1m USB-C to Lightning Cable

Hello,

I ordered a 2m USB-c to lightning cable from the Apple store because the longer length was more convenient than the 1m USB-c to lightning cable that came with my iPhone 11. However, when I was charging my phone using the 2m cable (and using the 20W wall charger bought from the Apple store), I noticed that my phone wasn't charging as fast.

I tested it:

• The 1m cable charged my phone 10% in 11 minutes (71%-81%).
• The 2m cable only charged my phone 5-6% in 11 minutes (81%-86%).
• Both tests were done using the same power outlet and the same 20W wall charger. All products were bought directly from the Apple Store.

Interestingly enough, I was using my phone for the first 3ish minutes when using the 1m cable, but I didn't use it at all while charging it with the 2m cable. Yet, the 1m cable still charged my phone around twice as fast in the same amount of time.

Is this a defective cable? Or is the 2m cable expected to charge devices more slowly? I was under the impression that they should charge at the same speed.

Thanks in advance for your help!