Checked and you’re right, it’s stated as a heavily caveated possibility, not an accepted way
Thankyou for the info, I’m deep in those docs at the moment figuring out why a flat meshified tilemap isn’t classed as walkable (bit offtopic but if anyone has any ideas 
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Your response doesn’t quite answer my question though : I wasn’t sure what if any issues / perf this might cause. My gut and a quick goggle suggests avoiding islands may lead to better performance.