Sorry but there is little you can do - changing the head for one with fewer or smaller nozzles may allow you to 'project' water further, if that's what you want.
The logic is this:
As you know, water is heated 'as required' with electric power showers. There is a fixed relationship between the electrical power going in (8.5kW) and the heat coming out (the product of the volume of water x the temperature rise given to the water by the heater).
This is why, when you turn the temperature down on these showers (for the same setting) the flow rate increases. What is happening is that the restrictor valve inside the unit is restricting the water less, meaning more comes out per minute, but at a lower temperature.
There is a certain illogicality about your previous situation before and now - because you say you have uprated the shower from 7.5kW to 8.5kW. Of course should mean you get a greater flow rate for the same temperature of water.
Which is why I say you might get more shower power if you change the nozzle.