Sounds like you’ve got the same ashp and cylinder as us then 
Getting the data into the emonpi requires some surgery on the ‘remote’, a bit of soldering, an esp8266, and an Arduino… Happy to give you some pointers on this, but I suspect it’s warranty voiding, so you may be better off watching the meter reading and outdoor temperature to give you an idea of ‘better’ or ‘worse’ for each change.
More volume is always better. On our system, most of the cycling was down to the wall thermostat, which implemented something called TPI - a method suited to oil or gas boilers, which uses fairly short on/off periods to try to keep room temperature more constant (the idea being that a more constant temperature can allow a lower average temperature, reducing consumption) This doesn’t play nicely with a heat pump, we noticed a big improvement by changing this for a thermostat that didn’t do TPI.
We don’t get much dT either, approx 2degC is normal. I’ve not been able to determine if the ‘8k’ route of thumb means ‘max 8k’ or ‘min 8k’, but my own musings suggest that the dT should be minimised (heat out of the ufh/rads is roughly proportional to the mean temp, but heat pump cop will increase as follows temperature increases, so we try to maximise mean temp while minimising flow temp)
The other large improvement we saw was reducing the flow temps - ours were set very high, and reducing them closer to MyForest’s numbers above made a huge difference. The method I used to ‘optimise’ our temperatures was as follows:
Set min and max outdoor temperatures to something reasonable (I’ve got our min as -5, max is +18 - below min the flow is set to max temp, above max the heatpump won’t run)
Flow temps can be set based on estimates of heat required at those outdoor temperatures, and the flow temps required to get that power (based on floor/rad area)
If the flow settings are too low, the heatpump will run constantly and the room won’t reach temperature. If too high, the heatpump will cycle and the floor/rads may get hot then cold.
Over a few hot/cold days you should be able to get pretty close
Aim for the ‘slightly too warm’ side - the extra power will cope with heating the house quickly (if you choose to have a lower temperature setting overnight, for example) and with windy/dark/etc days where losses might be higher.
Mixing rads and ufh can be difficult, depending on setup. If the ufh was installed assuming a standard boiler, it’ll probably have mixer valves to drop flow temps from 70-80degC from a boiler to lower temps for the floor. This can reduce efficiency a bit with a heatpump. Equally, if flow temps are set to suit the ufh, then the rads may not do much unless they’re very large. As yours are upstairs, that’s probably not a huge issue. I don’t have ufh here yet, so can only really recommend that you do some reading about ufh with heatpumps (I did read a few while doing my own research, but don’t have the links to hand at present, sorry)
Hope that helps get you started