After a reboot the readahead values are changed

Issue

We set the readahead values via lvchange -r, but it seems that after a reboot the value is not the one we set. For example:
The default readahead is 1024:

[root@server]# blockdev --report /dev/dm-6
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  1024   512  4096          0       536870912   /dev/dm-6

We change it to 512 and the change is correctly displayed:

[root@server]# lvchange -r 512 /dev/mapper/vgdata01-ltest
  Logical volume "ltest" changed.

[root@server]# blockdev --report                         
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw   512   512  4096          0       536870912   /dev/dm-6

But after a reboot we observe a different value:

[root@drtbrt ~]# blockdev --report /dev/dm-6
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  2048   512  4096          0       536870912   /dev/dm-6

What is the reason for the discrepancies?