Bloom will respond to lighting conditions, emission and brightness of material.
The bloom pattern is a post processing effect meaning you do not have direct control of it other than that provided via the puzzle.
However, if you want to have an area affected by Bloom, you can do a few things:
1. Add geometry to the area you need to be affected.
2. Increase the emission of the surrounding materials
3. modify the lighting in the area to manipulate the appearance.
These methods require you to experiment and tweak and readjust sometimes 100s of times to get the effect you are looking for. Its will be up to you how much effort you want to put in.
As an experiment I would suggest you try various single shapes, rectangles, cylinders, spheres, etc and render those out as single objects and test in a V3D project and understand how the shape of the objects affect bloom and what the actual bloom pattern is at the scale/strength you want. Bloom effects can look circular but can also look square depending on camera distance and size of the object.
Bloom is a tool we have but it will be up to you to determine if it’s the right tool for your needs and if it is….you will need to experiment with it a lot.
The alternative approach are sprite sheets discussed earlier.