I’d suggest leaving modulation enabled. It allows Madoka to override the flow target temperature based on the indoor temperature. A value of 10 corresponds to roughly 3c rise or fall in flow target. See this post for more details.
The first and best thing you can do is dial in the weather curve. The best times to do it are when its around freezing for a couple of days, to set the lower end, and then again when it’s milder, say 14c. But as a starting point, try 42c at design temp (usually -2 or so) and 28c at 13c. You’re aiming to find the point the house stays roughly at the same temperature on cloudy days without too many other indoor heat sources (cooking etc).
You should find a few things happen:
- The compressor works much less hard now it’s target flow temp is lower. It should do the low and slow you’re expecting.
- The indoor temp should stop increasing and shooting past your desired setpoint. Modulation will help govern this and compensate for sunny days, cooking/human activities etc.
- Running costs and COP will be much better.
There’s no real difference between using Madoka for control versus LWT mode in this regard since the goal is to produce just enough heat to compensate for the heat loss only. The Madoka is just there to guide the flow target temperature. There are other Madoka quirks you might find over time but for now, getting your WD setting right is top priority, IMO.