Is there anyway to generate animation curves rather than linear interpolation for the layer offset? I am generating a time tunnel effect, sketching using the rings 2 preset and I want the mouth of the tunnel, ie. that closest to the camera to remain centred. Any help greatly appreciated.
No, layer offset is straight line only. I'm not sure exactly what you're trying to do, but you can import keys into the layer offset. Get the data from After Effects (or any other compatible system), making sure you have a key at every frame. Then when you import into the layer offset data, you'll have a curve (if your original data in AE was curved).
You can test this out by placing an emitter, using "record position" to create some curvy path, then export the position data to the clipboard, then import the position data to the layer offset.