I'm not 100% sure what you are asking here, but I'll link the Breville manual and point out some pages that may help you since I want to try and help a fellow coffee fan. https://www.appliancesonline.com.au/manuals/bec300w/bec300w_operatinginstructions.pdf
Page 8 deals with coffee preparation.
Illustration 9 states:
To stop the coffee flow before touch the lit control or move the slider towards the back of the machine until it stops.
To manually top up your coffee, touch any of the controls within 4 seconds from end of preparation and touch lit control again to stop
To change the selected cup size during brewing select the new desired control. The machine will stop immediately if coffee volume extracted is larger than new desired control.
Page 9 deals with programming the water volume, and I feel like this may be what you are wanting to know.
Any control can be programmed. Completely open the slider and insert a Nespresso capsule.
Touch and hold the control while closing the slider. Release control when desired volume is reached. The other 2 controls flash for confirmation. Water volume level is now stored in the control used during programming.
Press and hold the Espresso & Lungo controls together for at least 4 sec. The other control flashes for confirmation.
To the side of those illustrations is the following note:
Factory settings are: 1. Lungo, Espresso, Ristretto controls 110 ml / 3.7 oz, 40 ml / 1.35 oz., 25 ml / 0.84 oz. 2. Automatic Off mode after 9 minutes. 3. Most frequently chosen cup size as Espresso control at 40 ml / 1.35 oz.
Happy coffee drinking!