Rain refuses to motion blur

Hey folks. Experimenting with rain in Eevee, at present using a ‘realistic’ rain drop shape, eg.
At the moment, this is my result:

(Full render to the left) - As you can see, several of the rain drops appear as if not in motion. The particle object can be seen at the end of the road (the glassy dome).
My current motion blur settings are as follows:
Any clues? Clearly I’m a newbie when it comes to motion blurs.

Motion blur requires previous frame and current frame to calculate the in betweens

It appears that you are at first frame in the timeline.