So, you're saying that it will only help if you are in a caloric deficit or if it puts you into one?
Say you're own maintenance, to keep it simple, is 3,000kcal. Your diet puts you at 2,500kcal. The ECA might might burn an extra 250kcal throughout the day so now your down to 2,250kcal.
Or, if you're diet is right at 3000kcal and the ECA puts you down to 2750kcal. Either way you will be in a deficit and losing weight (hopefully fat).
The main point I'm asking about is if you're (hypothetically) 1,000kcal over maintenance, would and ECA help to burn fat even though you're still in a surplus?