I’ve come across this bug that was reported a few times before, althought they were not in the bug reports section:
I’ve tested in 4.12 and 4.13 and the problem persists, it happens when we change the distribution of the “strength raw” to a parameter, changing the parameter will not change the strength which will always default to 0
Can confirm that this is not working.
And that makes me a sad panda.
Hey Esteves and Luos,
Thank you for confirming this issue and bringing attention to other Answer Hub posts. I was able to reproduce this issue and have submitted a bug report here: Unreal Engine Issues and Bug Tracker (UE-35165)
You can track the report’s status as the issue is reviewed by our development staff. I also made sure to add a private comment bringing attention to the other posts to show community interest.
again,
Hi Ed, thank you very much for the update.
On the bug report you mention that you exposed the radius as well? can you tell me how can I make the radius editable via blueprint? I might be able to use that as a work around while waiting for the fix
I don’t think the radius is what you are looking for since it just changes the spawn location. I created and attached a project that fakes point gravity and exposed the parameters for spawn sphere “Radius” and “Fake Gravity” (controls velocity of particles). Use a negative value for the particles to flow inward and a positive for them to flow outward.
for the example, but it works only in really special cases, so I am surprised it wasn’t resolved for so long time. and even the ticket was closed now 
As an addition if I want to set/get the parameter by C++ with SetFloatParameter/GetFloatParameter it will crash the engine.
Anybody has a good workaround?
Bump, still an issue in 4.25