Things were different with 1e fireballs, such as the one depicted on the iconic Erol Otus artwork depicting a magic user poised to vaporize a green dragon with an actual green ball of fire in her hand. That type of Fireball was an increasingly expanding cannonball of fire, capable of cooking everything in its path from the point of origin to point-of-detonation. It had no backblast and was great for clearing a tunnel full of bunched-up mind-flayers leading a goblin army. 5e fireballs function more like modern military missiles in that they arm themselves on detonation. Therefore, something standing in the path of the streak of flame shooting out of your finger but out of range of the detonation is subject to damage from the flame, not the detonation. It's up to the DM to determine whether obstacles are damaged by the flame, whether the flame harmlessly passes through them, or whether obstacles prevent the streak of flame from reaching its target, preventing its detonation. If the lieutenant orc in the example above, however, places his living orc shield at the approximate point of detonation while standing 1 foot back himself, then the lieutenant is no longer exactly at the point of detonation, and the unfortunate living orc is. In this DM’s humble opinion, the callous orc lieutenant would be allowed a Dexterity saving throw to halve the fireball damage for himself.