When you set the devices to be the same extension (wave, desktop, etc.), then they all have the same identities and settings. In essence, they function as if one and regardless if being a member of a ring group or Q agent or other. If you pause, you pause all. If you log out with one, you log out all and the list goes on.
The determining factors are the method of membership be it an account with more than one device, q, ring group.
How a function is induced - by a dial code or if using a device independent function.
As an example, if using a dial code then it depends on where the dial code is executed. In some cases there are codes that are specific to the UCM and others, if features are enabled at the phone, will only take effect at the phone.
For example, if one uses a DND dial code that is activated at the UCM, then when a call comes in, the UCM will know that DND is activated and will not send any call to any associated device. If however, DND is not activated at the UCM, but at the phone instead, the UCM will pass the call to the device and the device will inform the UCM that it is not taking calls. The device buzz or chirp one time upon seeing the call initially, but it will stop almost immediately following the UCM seeing the reply sent by the phone telling the UCM it is not going to take the call.
The options are too long to go into here, but what you might try is to simply have the user set the phone WAVE to DND using the account status function using the Wave app. This is a apparently a device only function. When a call comes in, the UCM will send the call, but the device will chirp/buzz and then stop. The desk hard phone will ring as normal. The down side is the chirp/buzz and then, of course, getting the user to remember to disable the DND when the time comes. Overtime and after a few friendly reminders for the forgetful - firing squads, public humiliation, dunce caps, perhaps they will more mindful. Just remember that DND is not an equal opportunity DND as no calls will come through and ring regardless of what or who sent them.
Play with the various settings and select what seems best for your needs.