The honeymoon period, if that's the right phrase, is very much an exercise in line drawing and judgment. I don't think there's any way around that. The four-year period is a reasonable adjustment frame for corporations or affected trusts to rearrange their affairs. To let it drag on would let the problem fester unnecessarily.
If you think about the old capital allowance rules where you only got to claim 50% appreciation in the first year an asset was acquired, why not 49% or 51%? As I said, it's an exercise in line drawing and not everyone's going to be happy with it.