SSD benchmarking with fio - write cache confusion

I am looking at some SSDs and try to benchmark them. In particular, I wanted to see if I can reproduce the numbers in the datasheet. Currently I am looking at a HUSSL4040BSS600 SSD which is SAS. With this particular SSD, I can enable or disable the write cache of the disk, using sdparm. With

sdparm /dev/sdb -p ca

one can query the write cache, and I get the cache status, and according to the output

Caching (SBC) mode page:
  IC            0  [cha: y, def:  0, sav:  0]
  ABPF          0  [cha: y, def:  0, sav:  0]
  CAP           0  [cha: y, def:  0, sav:  0]
  DISC          0  [cha: y, def:  0, sav:  0]
  SIZE          0  [cha: y, def:  0, sav:  0]
  WCE           1  [cha: y, def:  1, sav:  1]
  MF            0  [cha: y, def:  0, sav:  0]
  RCD           0  [cha: y, def:  0, sav:  0]
  DRRP          0  [cha: y, def:  0, sav:  0]
  WRP           0  [cha: y, def:  0, sav:  0]
  DPTL          -1  [cha: y, def: -1, sav: -1]
  MIPF          0  [cha: y, def:  0, sav:  0]
  MAPF          -1  [cha: y, def: -1, sav: -1]
  MAPFC         -1  [cha: y, def: -1, sav: -1]
  FSW           0  [cha: y, def:  0, sav:  0]
  LBCSS         0  [cha: y, def:  0, sav:  0]
  DRA           0  [cha: y, def:  0, sav:  0]
  SYNC_PROG     0  [cha: n, def:  0, sav:  0]
  NV_DIS        0  [cha: n, def:  0, sav:  0]
  NCS           0  [cha: y, def:  0, sav:  0]
  CSS           0  [cha: y, def:  0, sav:  0]

and the explanations in this document on page 281, the write cache is currently enabled (WCE=1). According to the product manual of this SSD, it should have the following specs:

so for example, with 4K random writes and QD1, I should get around 11K IOPS. I test that with the following fio command line

fio --name=iops --rw=randwrite --bs=4k --iodepth=1 --ioengine=io_uring --direct=1 --fsync=1 --numjobs=1 --time_based --runtime=20 --group_reporting --filename=/dev/sdb

and fio reports:

write: IOPS=4197, BW=16.4MiB/s (17.2MB/s)(328MiB/20001msec); 0 zone resets

This is quite a lot worse than the specification of 11K. So, now, for test purposes I will disable the write cache of the SSD

sdparm --set WCE=0 /dev/sdb

and run the exact same fio command as above, and now I get

write: IOPS=11.8k, BW=46.0MiB/s (48.2MB/s)(919MiB/20001msec); 0 zone resets

so actually spot-on to the specification. However, I don't understand this behaviour. Why is this the case? why is the SSD faster if the write cache is disabled? and furthermore, if I am using this SSD to run VMs from it (which will give a high IOPS demand) should I, therefore, set WCE=0 to have better IOPS performance?