Dell E6320 and PXE boot with WDS legacy mode

At a costumer we came across a problem with a Dell E6320 booting with pxe.
It did not respond to the PXE server and therefor waited indefinetely on the boot agent screen.
In the current environment (flat network) there are multiple pxe services configured, one for Citrix PVS and one for WDS.

Because there are timing issue for response, a pxe response delay was set on the WDS Server. It had to respond later than Citrix PVS. The delay was set to 12 seconds and worked fine for all desktop and mobile models at that time.
With the new Dell model we had to tweak the response value. The lowest delay we could set it to, and that it respond well, was 4 seconds.

You can set the delay trough one of the following ways:

WDSUTIL /set-Server /Server:<servername> /ResponseDelay:60
Where 60 is the wait time in seconds

Or trough a registry  key

The value is also set in seconds.
After you changed the registry key, the Windows Deployment Services (WDS) Server services has to be restarted.