Particle Visibility inconsistent

Hi Everyone.

Today I want to make a Rocket thruster, but have no idea how the Niagara system works, so I thought I go study a bit on it.
I’ve created a completely blank niagara system to learn about this.
I found a wonderful tutorial on YouTube that explains Niagara from scratch (for reference Beginner guide to Niagara)

Unfortunately, I’m getting a bit confused about a random result that I’m not expecting.

The tutorial explains about the opacity of a sprite over it’s lifespan, where 1 is completely visible and 0 is not visible, so far, that makes sense to me.

So under particle update, I’ve created a scale alpha with a float from curve to make the sprite disappear gradually over the looping time of 5 seconds.

But, if I press play in the timeline, the sprite disappears, pops in existence and then starts shifting in and out of existence (visually).
If i turn the values around (eg start 0, value 1-end 1, value 0) then it works fine and I can see the particle become visible gradually.

If I reverse the values again, I’m getting the unpredictable behaviour I just described.

Maybe I’m doing something incredibly stupid again, but it’s a bit difficult to learn something when the results vary from the expectations.

Could someone please explain what noob mistake I’m making here?