Emptiness in Buddhism is a complex topic with different ways of viewing it. As a Buddhist, what is important is how these perceptions of emptiness affect our thinkings, decisions and behaviours. Buddhism is known for its pragmatism and practical approaches. I believe the geometric example of emptiness given in the OP is valid. However, I struggled to see its practical applications. Below, are some practical applications of emptiness.
Emptiness as a meditative dwelling. If we have a chance to go to a quiet park or a place where there is little human activities, we get a chance to experiment and experience this. Or if we happened to live in a place where there is winter, go to a large, open space after a heavy blizzard. Empty our thoughts and listen intently to the surroundings. We will notice the quietness in the air. Slowly, as we willingly stay with this quietness, we’ll notice our mind becoming very still. And the strange thing is the mind actually enjoys being in that state of stillness. No inner chattering, discourse and arguments about the past or future. Just being present and enjoying it. Honestly, this is one reason why I (and I believe many people) enjoy going to the parks and being surrounded by greeneries. I strongly believe if we can maintain this state of mind throughout the day, it will do wonders for our mental wellbeing.
Emptiness as an attribute of objects. If we are obsessed with wealth, material possessions, physical appearance and reputation, seeing the lack of self in these things (even in ourselves) helps to weaken this strong attachment. Who is going to inherit our wealth, possessions or remember our youthful and good looks after we are gone? Does it matter? Being around people who are constantly obsessing over money, power and appearances and also people who are nonchalant about these things; do you ever wonder why there are such huge differences both in attitude and behaviour over wealth, reputation and gain? When trying to understand the psychological make-up of these two groups of people (whom I know intimately) and I realized that fundamentally they have very different valuations of things. If we see possessions as intrinsically devoid of real value (i.e. emptiness) other than for sustaining our existence; would we become hysterical if we lose these possessions? Yes, I may envy the former group but the most enjoyable times were spent with the latter group.
Emptiness as a type of awareness-release. Personally, I don’t have concrete experience with this. But I believe this is a central theme in Mahayana tradition and must, therefore, been a source or an inspiration for liberation for many practitioners over the ages.
So, if there are practical applications in a geometrical definition of emptiness, it would be more relevant. With Metta.