Attempting to set IO resource limits on docker container doesn't work

Question

I am on a Ubuntu 22.04.4 LTS machine with Docker version 26.0.1, build d260a54. I am trying to run a container with IO (disk) read and write both rate limited to 50mb/s - this is a low priority container, and I want to ensure that it doesn;t hog the IO bandwidth, essentially. To do this, I am attempting to set this limit using the --device-write-bps flag when doing docker run. This is what the output of df -h on my system looks like:

Filesystem                           Size  Used Avail Use% Mounted on
tmpfs                                6.3G  1.2M  6.3G   1% /run
/dev/nvme0n1p3                        63G  6.9G   53G  12% /
tmpfs                                 32G     0   32G   0% /dev/shm
tmpfs                                5.0M     0  5.0M   0% /run/lock
/dev/nvme0n1p1                       256M  8.6M  248M   4% /boot/efi
ops.utah.cloudlab.us:/share           18T   22G   18T   1% /share
ops.utah.cloudlab.us:/proj/wisr-PG0  100G   54G   47G  54% /proj/wisr-PG0
tmpfs                                6.3G     0  6.3G   0% /run/user/20041

Experiment 1: docker run -it --rm --device-write-bps /dev/nvme0n1p3:5mb ubuntu /bin/bash. The root / is mounted on /dev/nvme0n1p3, so I would expect this to be the correct device to ratelimit. Inside the docker container I tried writing to file (and got the following output):

root@4fbcdf56adb0:/# dd if=/dev/urandom of="random_file.bin" bs=1M count="1024"
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 5.00586 s, 214 MB/s

Expected behavior: This file read should have had a throughput of 5mb/s, not 212mb/s.

Experiment 2: docker run -it --rm --device-write-bps /dev/:5mb ubuntu /bin/bash - maybe this will rate limit all devices? Output:

root@c03341b547da:/# dd if=/dev/urandom of="random_file.bin" bs=1M count="1024"
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.85882 s, 221 MB/s
root@c03341b547da:/# 

This, also, did not work. What am I doing wrong?