5th dnd – If an enemy is just below a ceiling 10 feet high, are they within melee range of a ground creature?

We met a group of vampires in the basement of an old church, up to three meters high. The first strike was mine, after which the creature attacked my ally and retreated to the ceiling as the deafening roar of my explosive blade punished his retreat. Still inexperienced and unsure of my reach, after a brief mental consultation, I decided to pass my turn to move to my trusty crossbow and take a little distance.

However, this turned out to be a mistake because just after, the creature was in my face trying to gauge my eyes. Thanks to my agility, I managed to avoid his attacks. Regretting my previous choice to change weapons, I was left with the choice between changing attack and missing a turn, attacking with disadvantage or using my crossbow as an improvised melee weapon and trusting Booming Blade to keep the enemy in place after my disengagement.

I should have had to change weapons, but I decided that 1d4 (improvised weapon) + 1 (magic ring) + 1d8 (powerful blade) was enough. I missed it.

On the plus side, it was the bolt assisted by my crossbow that finally managed to defeat the vampire by piercing his heart.

In this situation, would it have been possible to attack only upwards instead of going to the crossbow?

In session, it was something to look for later and decide, but I found no rules to attack in 3D.

With a height of more than 5 feet and a range of melee attack estimated at 5 feet, I should have been able to reach the ceiling itself, not to mention the vampire spawn that was hanging there.

As for the exact measurements, (read this section only if you appreciate unnecessarily to analyze too much):

My character is 5 feet 6 inches / 5.5 feet, which gives an estimated standing range of 7 feet 4 inches / 7.3 feet (for a human, my character is a Kenku), the blade of a sword short goes from 12 to 20 inches / 1. to 1.6 feet. This should give me a height of 8.3 to 8.9 feet of static.

By testing this in real life, my estimate of range and distance traveled is less than 0.2 inches from the estimate on the site and I am just shy to reach my ceiling standing statically. As a test, I tried to move as if I was attacking my ceiling and I could feel my hand touching the ceiling, the length of my fingers and the distance I was missing to reach my ceiling. I estimate about 0.4 feet of extra height. . Considering that I am taller than my character, let's say that it gives 0.3 feet, which increases the height from 8.6 to 9.2 feet and that does not change the way you hold the handle of the handle. ;sword. In addition, lying on the floor, my chest and legs are about 0.6 meters.

As my Kenku is not a human, but a humanoid, it is impossible to estimate the length of the arms that influences standing range, however, since birds usually have large wingspan and long legs, I think that 'It is reasonable to assume that the arms should be as long, if not longer than that of a human.

So, this would require Spawn Vampire to be flat against the ceiling without any room hanging more than 0.2 to 0.8 feet away for it to be out of my reach. I consider this improbable.

What are the real rules for this type of scenario or how do you manage it in your group? Should I be allowed to attack in melee an enemy who is at the ceiling or low in the air?