The question is whether once ignition is achieved there could be a way to design the target/geometry in such a way that the fusion reaction becomes self-sustaining/self-propagating.

The history of thermonuclear weapons leads me to think that the answer may be yes. There does not seem to be any real upper limit to how large a thermonuclear weapon can be made. In the 50's and/or 60's there were proposals to build GT devices. I don't think the fission trigger for such a weapon could have scaled by nearly as much.

So by analogy if a relatively small fission trigger can cause a fusion explosion that is many orders of magnitudes larger maybe one or more tiny laser induced fusion reactions could be used to trigger a much larger one.

If that were the case the efficiency of the laser trigger would be of little importance.