What’s your DHW flow rate (build pump) set at in the heat pump controller?
Can be 50% to 100% or Auto.
And what’s your target hot water temp? I’m assuming 47C ish from the graph?
Looks like your flow peaks about 62.
If the flow rate is low (or you have some sort of restriction) then the DT between flow and return will be wide.
And your target temp will always be below your return.
Imagine another line in the graph between the two existing lines, that would be return.
If you are a tinkerer, have you considered and ebus reader to get at all the values?