Seems to me you didnt get that large of an increase but any improvement helps. Try setting the round robin policy limits to IOPs, and set the limit to 1. Re-run your tests and see the difference 
This is what I run from PowerCLI to make the changes to the entire cluster and all the LUN's:
$Cluster = Read-host "Enter Cluster Name"
foreach ($vmhost in get-cluster $Cluster | get-VMHost){
Connect-VIServer -Server $vmhost.Name -User root -Password <yourpasswd>
$esxcli = Get-EsxCli -VMHost $vmhost.Name
$esxcli.storage.nmp.satp.set($false,"VMW_PSP_RR","VMW_SATP_SYMM")
foreach ($lunpath in $esxcli.storage.nmp.device.list() | where {$_.device -like "naa.*"}){
$esxcli.storage.nmp.device.set($null,$lunpath.Device, "VMW_PSP_RR")
$esxcli.storage.nmp.psp.roundrobin.deviceconfig.set($null,$lunpath.Device,1,"iops",$null)
}
}