FormControl lookup not opening on user input


I extended a formcontrol with a new lookup method, which works as intended.
In the UI the lookup does not open when the user types new information into the formcontrol, unlike the other formcontrols on that form.

I cannot find the documentation on how to trigger the lookup on user input, I attempted it via the onModified event but that equally only works once the user clicks outside the formcontrol.
How can I cause the lookup to trigger on user input?