When you're playing up front on your own (on the basis Byrne and Robert were wide) you can't close down in the same way - you need to hold your position that much more and leave it to the others to close down.
To be a little fair to a Smith, he's not a 100 percent match fit yet, did not play more than 45 mins during preseason, therefore think he was not chasing a awful lot, especially as he knew he was likely to be playing the full 90 mins