SKOS,
We were asked whether we wanted Area or Aerodrome and she said if pay was what you were after there are few tower jobs that have that high band of pay such as Heathrow. You are more likely to get that band in Area. In terms of hard, thats to do with validation, Heathrow has a high failure rate for validation compared to other places due to how busy it is. Does this help?
Seb