@dwuk This is not quite what I meant. I meant a interlacing pattern, wide enougth to weld together the sparse infill:
This way you should retain close to full part strength and can put all perimeters in a single thread for optimal surface quality. Scince the sparse infill appears to be generated in relation to a global origin, this should work for arbitrary models and infill patterns when in parallel printing mode. For parallel mirror mode, you need a infill pattern that is and stays symmetrical to your mirror plane regardless of z-height. From the more performant infill patterns, cubic appears to work, when angle is changed to zero:
You can ignore the d-dimension. I dont know why I thought having the interlacing that wide would have been critical. I put my files on a printabels site, if you want to take a look, but cant post the link here due to lack of reputation. Ill put it in a Youtube comment for now.