Benchmark throughput displayed is not the same than the one from vLLM

In many occasions, the throughput value detected and displayed by Benchmark is not the same value seen in the vLLM trace.

```
┌─────────────────┬────────────────────────────────────────────────────────────────┐
│ Parameter │ Value │
├─────────────────┼────────────────────────────────────────────────────────────────┤
│ Max VUs │ 128 │
│ Duration │ 60 │
│ Warmup Duration │ 30 │
│ Benchmark Kind │ Sweep │
│ Rates │ N/A │
│ Num Rates │ 1 │
│ Prompt Options │ N/A │
│ Decode Options │ num_tokens=Some(800),min_tokens=50,max_tokens=800,variance=100 │
│ Tokenizer │ deepseek-ai/DeepSeek-R1-Distill-Llama-8B │
│ Extra Metadata │ N/A │
└─────────────────┴────────────────────────────────────────────────────────────────┘

Run 1:

│ Benchmark │ QPS │ E2E Latency (avg) │ TTFT (avg) │ ITL (avg) │ Throughput │
├────────────────────┼────────────┼───────────────────┼────────────┼───────────┼────────────────────┼
│ warmup │ 0.07 req/s │ 13.95 sec │ 3268.06 ms │ 15.22 ms │ 50.42 tokens/sec │
│ throughput │ 3.84 req/s │ 24.96 sec │ 307.17 ms │ 36.85 ms │ 2560.47 tokens/sec |

Run 2:

Benchmark │ QPS │ E2E Latency (avg) │ TTFT (avg) │ ITL (avg) │ Throughput │
├─────────────────┼────────────┼───────────────────┼──────────--──┼───────────┼────────────────────┼
warmup │ 0.08 req/s │ 13.30 sec │ 1554.01 ms │ 14.70 ms │ 60.15 tokens/sec │
throughput │ 2.41 req/s │ 38.43 sec │ 665.35 ms │ 56.19 ms │ 1596.76 tokens/sec │

Trace from VLLM similar in both runs:
INFO 06-13 10:23:08 [loggers.py:111] Engine 000: Avg prompt throughput: 548.9 tokens/s, Avg generation throughput: 2475.0 tokens/s, Running: 128 reqs,
```
The vLLM trace just above is related to Run 2. I would have expected to see a value of 2475 tokens/sec or so in the Run 2 instead of 1596 tokens/sec.

Am I misunderstanding how that works?