Hi @Lachie,
Yes, this is possible. If you go to the Parameters tab and click JS (for Joystick), you can change the minimum and maximum possible gains, the default one on startup, and the number of gain steps. It’s also possible to set a custom multiplier for the throttle (vertical) gain 
This is currently documented in our Features while in Operation docs, which links to the relevant parameters. I only learnt about this recently myself, so I feel like it could be more obviously documented.
I’m thinking it could be worth mentioning on the Joystick and Motors setup pages - are there any additional places you think would be helpful?