ChemicalSprayerProjectileEntity originates on the west side of the player and does not rotate around, depending on player look direction. It's rotation is only influenced by Up/Down looking angle: when looking up - it moves to the south of the player, down - north.

Due to this, when moving in the direction, opposite of where it is spawned (projectile spawns behind the player) - there's very high chance of the player being set on fire by his own projectile.

Adding some kind of buffer time, where player cannot be set on fire by his own projectile at the start, can be helpful too, because now you'll be set on fire when moving quickly even if projectile starting point positioned in front of you. Or just spawing projectile further from the player.

Offtopic suggestion: limit duration of the ChemicalSprayerProjectileEntity so it would burn up when traveling for too long.