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.Not to worry about that ∆. The delta is always moving a bit until you reach thermal equilibrium. The point when temperature has stabilized, not increasing or decreasing across the loop. At that point you should be at design ∆. Probably most systems never are, as @Kaos suggested. It is rare that an installer checks these numbers. It could take hours, days, for a large concrete slab to reach thermal equilibrium on cold start up.

Lower delta= higher heat transfer rates. It does cost a small bit more pumping, and you want to stay below 5 fps velocity to keep things quiet.

Here is the rational for the increased output:

You would need to get up around 8 gpm in 3/4 M copper to exceed 5 fps

Idronics 23 is a good read for understanding heat transfer in Hydronic systems

Lots or residential insyallers that want to know or check flow rates install Quicksetters as you do not need a $3000.00 B&G delta P meter to read them :)

I think your neutralizer is upside down, the outlet wants to be high to hold back a reservoir there, for more neutralization time,

Lost the install manual already? That's not good. There are on-line copies.

https://www.navieninc.com/products/ncb-240-110h/downloads

There are also wiring diagrams in the Appendix

Page 43. Thermostat all three wires (Ecobee or NEST) I would probably use Zone 1.

Page 43. Circulator

Has this all been done ?