Here’s my armchair guess

I’m not sure how much of a direct hit vs shrapnel hit to destroy these are… but if it’s flying upwards and misses the shrapnel will have upward momentum while the target has downward momentum, making a miss be a complete miss.

If they come back down on their final hit trajectory, they can gain a bit more speed on the downward, while also keeping the shrapnel from the explosion heading downwards, making a potential hit more likely.