That is because of the particle's Life is 1 second by default (you can change that in the spawner's script Life = 2; for example)
LifeRatio is the particle's normalize age, when the particle spawns, it has a LifeRatio of 0, when it dies it's 1, so no matter what you plug in Life, LifeRatio will always be [0-1]
You can try Position = Path_1.samplePosition(LifeRatio); and try tweaking the Life, it should modify how fast the particle moves along the path
You could also use, spawner.age, scene.time, Age which are other helpful properties
Cheers