I use to run my bell on the center top of my handlebars, near the stem. This is a typical bell position, but it requires moving a hand off of the brifters to access it. Situations where one needs a bell are often situations where one also wants to be ready to brake or shift.
A couple years ago, I saw someone position their bell on the hook of the drops. I thought that was a great idea and promptly copied it. The positioning is ideal. It allows me to keep my hands on the hoods and actuate the trigger of the bell with my pinky, while the rest of my fingers interact with the brifters as needed. It is high enough in the hook that it does not interfere with my hand placement while riding in the drops, though it does require releasing the hold on the bar to actuate it from down there. But that is still a smaller movement than reaching from the drop to the center top of the bars. I spend about 90% of my time on the ramps and hoods, so that is the interface I optimize for.
I strongly recommend setting up your cockpit such that you can flick your ding-ding without sacrificing the drive controls.