What M@L said can depend on your range and your goals.
If you've got quite an aggressive goal and wanting to lose as much as you can as quickly as you can, you will probably never leave the 1200-1550 range, no matter what your exercise goal says. It can take thousands to move that, because your goal may simply be too aggressively fast for your weight.
If you have a more adaptive goal that is not the minimum, eg 1270-1620, then this should change with any, even quite small, increases in fitness. Eg if you add an additional 350 calories exercise to the burn goal, that is 50 more calories per day you need, so your range will increase by that.
Deb, in New Zealand