Keep particles rendering even if off the screen?

I have an RTS style game with units that you move around the map. The particle effects (like thrusters on a ship) stop rendering when the unit is not on the screen, which makes sense of course for optimization.

The problem is I have a 2d scene capture camera that shows the player a “live portrait” of the unit currently selected. If you click the unit to fly across the map for example, when it leaves the screen the particles stop rendering for the 2d scene capture camera.

I can’t actually find the settings that determine when/if particles are culled in the first place. Hopefully someone can shed some light please!