https://cdn.discordapp.com/attachments/492712536702058496/801553763370139679/unknown.png

Length of red lines.

An easy method, in my opinion is to place guides at the locations desired for handle distance. When dragging the handle, it will snap to the guide. For more precise location, you can place a pair of guides and snap to the intersection. You can create a construction object in place of the guides if doing so makes it easier to identify location and rotation.