Issues with mounting nfs share with rsize and wsize options

Hi all.
I´m remounting a StoreOnce NFS share, that was mounted with the value 1024000. Due to performance reasons, HP´s recommendation is mount the share with r/wsize = 512000.
When remounting the share omitting the -o option before r/wsize parameters, the values persists to 1024000 value. When parsing the -o option to mount command, and rsize/wsize = 512000, the share is actually being mounted with rsize and wsize = 262144. (Checked with mount -l).
Command sample:
$ mount -t nfs4,wsize=512000,rsize=512000 /backup → by this way, the value persists to 1024000.
$mount -t nfs4 -o wsize=512000,rsize=512000 /backup → by this way, the value goes to 262144.
$mount on /backup type nfs4 (rw,relatime,vers=4.0,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,,local_lock=none,

*There was no entry in fstab file, so, I created an entry with the 512000 value, but this not changed nothing.
Any hint on it?
OS: SLes 12 SP 4
Thank you all.
Marcos A.