Tremolo beam placement

The online help shows a tremolo with half notes like this, which is fine.

I want to add a tremolo with whole notes, so I entered a pair of half notes like this ...

... then I added a tremolo, which looked like this ...

... then I tried to improve the placement of the tremolo, and I was able to adjust the slope (by dragging the end handles vertically) and move it vertically (by dragging the middle handle vertically), but I can't move it horizontally (none of the three handles will move horizontally) so it doesn't obscure the first note like this ...

How can I adjust the horizontal position of the tremolo so it fits between the notes with space at both ends, like the example in the online help?