Why wider stripe leads to lower encoding throughput even with same parity?

Hello!

I did some measurements with erasure coding, and I found that EC with a wider stripe usually has a lower encoding throughput. For example, 10+4 has throughput of 6989 MB/s, but 20+4 has throughput of 5467 MB/s.

Is it expected and is there any explanation on how this happens?

I thought EC configurations with same parity numbers would have similar encoding throughputs.

Thanks!