I don't know whether it'd be going too off topic, but you might want to examine the different types of annexation: for example, the structure concerning 'express' annexation is far more satisfactory in terms of favouring the covenantor (in absence of contrary intention, it will be assumed that annexation attaches the benefit - Federated Homes v Mill Lodge) then 'implied', where the 'burden of proof' (so to speak) is reversed, and it will only be when there is an extremely clear intention implicit in the circumstances that it is granted (Marten v Flight Refuelling) so the balance is tipped in favour of the covenantee (in that the benefit is less likely to be given). Of course, remember that under s.78(1) LPA most covenants will now be annexed automatically to land, even where there are no express words, so cases where this fails will be few.
Don't know if that helps at all...is this a random essay question you've been sat, or one you're trying to practice from an exam paper? If it's the former, then it probably would help to mention the 'old law' before the legislation in a bit more detail then if this is a practice exam question, whereby you might just want to say that in the past it was slightly harder to prove annexation if it wasn't expressly stated, but this hurdle has been overcome by the 'new' statutory provisions.