This would depend on the size and complexity of the form/application.
We can keep it simple until the code uses fixed values and stretches to minimum lines.
Listing few points below, if answer to any of them is 'yes' then it would be better to separate the concern.
- You have started to repeat the code.
- The logic of finding the position is complex e.g. calculate using certain algorithm.
- It needs to talk to external interfaces, e.g. get size of display, find a value saved in database etc.
- The form code has grown substantially because it is doing many other things apart from positioning e.g. data binding, event binding, handling display etc.
- You want to write unit tests for the form and want to mock the form position.
- You want to unit test the form position.
This would be a minimum check before I decide to keep the code in same class. But I also remember that it might not be valid in all the cases. When in doubt I would go for the simplest solution.