Having been to all our Championship games bar one, I would say that yes, on balance, the defence has shown some improvement
HOWEVER we are still prone to basic individual errors / switching off, call it what you will. Last night at Derby was a good example - the 5 or so minutes after HT Derby, who we'd kept pretty much under control in the first half, strolled through our back 4 twice, hitting the post first and then scoring
That said conceding is frequently not just the back 4 making errors - it can also be about the midfield not offering sufficient protection. I don't think that the constant changes in formation and starting 11 is helping. We seem to lack rhythm, and there is a tendency to revert to hoofball when under pressure