Yes I did make the change to a dT of 4 (from 5) and I would say that it has slightly improved COP and slightly reduced energy consumption which is definitely a win:win!
As you mentioned, I see my 6kW unit modulate flow rate much more readily with this lower dT, before it would just stick at the lowest possible flow ~6.75 l/min.
I’d like to further reduce to a dT of 3, to see what impact that has. But before making that change, it’d be really useful if the ability to compare a system on heatpumpmonitor.org was working again (to empirically compare the data of the system to itself, rather than going from gut-feel and assumption).