@henk-herck - thanks for your reply and suggestions.
I changed the pins to output and set them as high, but unfortunately it didn't change the outcome. In the end I soldered some wire into the OpenSprinkler's expansion board to help me get to that row of pins which allowed me to work around my issue.
I'd never really looked at the Orange Pi range before and went a bit down a rabbit hole looking at them yesterday. They're quite interesting and I'll look into them a bit more today.
@TRS-80
Thanks for your reply 
If I get the energy I might move away from DietPi, but unfortunately I have a lot to do at the moment.
Hi,
I recently set up an OpenSprinkler that's using a Raspberry Pi and thought I could use it for more, then I found MySensors and now I think I have a new hobby It's all very impressive.
I've connected up a nrf24l01 module to the Raspberry Pi and followed the guide, but I found that the rpi would only successfully connect to the nrf24 when I'm using the default CS and CE pins. When I try to change their pins using --my-rf24-ce-pin=33 --my-rf24-cs-pin=37 with the configure script, it didn't appear the change the pins as the rpi would fail to connect to the nrf24 on those pins, but could still connect with the default pins. When the make is running, I can see it launching g++ with -DMY_RF24_CS_PIN=37 -DMY_RF24_CE_PIN=33.
I also tried directly editing the MyConfig.h file to explicitly define the values, but that failed to work as well.
The OpenSprinkler RPi PCB board and case makes it harder (but not impossible) to access the back row of pins which is why I was trying to use non-default pins in the first place.
If I add --extra-cxxflags="-DMY_DEBUG_VERBOSE_RF24" to the configure script, then when I run a test, it includes the output:
DEBUG RF24:INIT:PIN,CE=33,CS=37
Which suggests that the software knows that's I've specified alternate pins to use.
I'm using DietPi distribution, btw. It does some things a little different which complicates things.
Does anyone have any suggestions?
To be honest, I'm happy enough to just use the default pins at this stage but this might help anyone else that finds themselves in the same situation.
Cheers,
Konrad.