Loving the new array modifier. Im playing around with using it in a little spline IK controller rig (which i think could make for some really interesting use cases of the modifier is expanded slightly) and im seeing this behaviour where if the spline isnt long enough, it leaves a gap which is to be expected.
There should be an adaptivity setting to make it more like railclones adaptive mode where it will adapt the scale of everything if the space available is above a certain percentage of the objects size. i.e. the object will stretch up to 10% before the modifier adds a new object.