Some advice and ideas please Failure to get right up to the back in plain hunting or in method ringing is a very common fault. Certainly better bell control is required, plus listening skills to identify that the bell is too close to the bell it is following because it is getting up to only about 4 and a half instead of right up to fifth place in doubles.
One point to note about this 'not getting up enough' progression that goes 1, 2, 3, 4, 4.5, 4.5, 4, 3, 2, 1 is that the change of speed between hunting up and down is spread over more blows. The change in position during this faulty process goes +1, +1, +1, +1, +0.5, 0, -0.5, -1, -1, -1, -1 (instead of the required ... +1, +1, 0, -1, -1... at the top for accurate striking). The faulty version therefore requires much less effort, as it consists of a larger number of small changes rather than the greater change of pace that is needed when changing direction accurately. The faulty process involves less effort and less anticipation, so can easily result from poor bell control.
I would suggest Kaleidoscope and similar exercise, starting with long places. Stand in front of the student as they ring perhaps 3, 3, 3, 3, 4, 4, 4, 4, 3, 3, 3, 3, 4, 4, 4, 4, 3... The aim is that they move directly from 3rd to 4th position, and then stay in 4th (rather than not going far enough at the change and not really getting up to 4th until the second blow there). Once the student has the idea of what to do, insist on really accurate striking. Ensure (by warning them in advance verbally or by gesture) to anticipate, so for example making a stronger pull on the fourth blow in 3rd place so as to be able to let the bell float up, giving the required extra delay to that it comes down accurately in 4th place. Only when they can consistently do this with long places, move on to just two blows in each place, and then revisit plain hunting.
You'll probably need to repeat the process when the student starts method ringing with dodges, as they will likely do 'lazy dodges' not getting up or down far enough at the dodge.