It is not the root system that is of concern, it is the canopy spread. Even some dwarf forms can develop to become quite wide (Crimson Queen can eventually reach a 12' spread) and that can interfere with walkway access. Of course you can always prune back but I dislike any excessive pruning on JM's and hacking away to reduce canopy width never provides for a good aesthetic.

So site with enough distance provided to accommodate the mature spread of the tree with unobstructed access to the walkway. The roots and the walkway are a non-issue :-))