I only noticed this with Antigua or magnus, never knew it was part of the blaster lines as well.
Blaster lines are currently the most powerful guns in LD today due to the variations (not overpowered like pulsars were, just powerful, and easily spammable), so I guess this is a good thing?
Some guns (notably blasters) have an element of randomness. If you shoot upwards you'll notice they also vary in spread too. Whether this is intentional or not I don't know. I can't say I really like it.
The distance might be something to do with frame times.