Do not adjust anything yet. The tendency is that the temperature is still rising, and the outside temperature is lower.
What does tilting the window mean in terms of time?
Briefly for 5 minutes or tilt permanently? With a permanent tilt position, of course you are heating outside as well, and your entire heating load calculation is no longer accurate because the heat loss to the outside is greater.
It may be that the underfloor heating feels like it reacts differently because the flow rate and thus the heat output is probably faster.
How was the consumption?