By middle I mean the middle of the grass square, in between decking and raised part.*
I have a Kilmarnock willow out the front of our house and I really like it but we have it in a border to provide some privacy (at least in Summer). It's not a feature plant to my mind as it will look very bare in winter.
I'm afraid I find them very boring and rather ugly most of the year. Being a willow they need lots of moisture to do well but can then grow their stems far too long for the height of the stem onto which they've been grafted. They can also be short lived. I was very relieved when ours died after a cold spell and so was a friend who lost hers to a dry spell.
It's also not a good idea to plant any of teh willow family near drainage and water pipes as their roots will go seeking moisture and can do expensive damage to pipes.