Editing a formula in a cell should not overlap the neighbouring left and right cell
When you type a formula in a cell, the full formula is displayed in the grid. If the formula is long, is starts overlapping with cells on the left and right of the edited cell. But it then means you cannot insert the coordinate of these overlaped cells in the formula by clicking on them because what you actually do is click on the formula. When editing a formula in a cell, the display of the formula must be constrained to its cell borders to allow neighbouring cells to be accessible for the click.
Kenneth Barber commented
This would of course force you to edit long formulas through the formula bar. When the formula starts covering cells that I want to click, I usually click near the cell and use the arrow keys to navigate.
David Tetard commented
To reproduce, try to enter that formula in a cell of coordinated B2 of standard width where all coordinated are entered by clicking on their cells:
You won't be able to enter C2 by clicking on that cell (the caret will go in the formula, not insert the cell's coordinates), you will have to manually edit the formula.