Hi @Ilas
Ok firstly i must point out that EventTick is perfectly fine to use for many things, and there is alot of stigma saying you shouldnt. Used right, optimaly it can be efficient and your friend.
BUT it looks like you are sending a 1 time event to update your emitter. So begin play should be fine for this. So as long as those user variables are spelt correctly there should not be a problem.
However you are better to test the theory , by firstly:
Use hard values instead of those parameters to eliminate that is not the issue. Try HIGH values which would look noticebly different ro make sure also.
If you dont notice any change then possibly the event play is hitting at your niagara system before its initialised so it doesnt get the new values.
Use event tick to test this theory. If that is the case you can still use begin play. But instead of putting the code in there, on begin play create a timer maybe 2 seconds to start with none looping. Let the timer run your update code.
If this works then shorten the timer as much as you can as long as it still works.
Have you checked your logs to see if there are any errors (click the filter button in the output log window and u tick messages so you only see errors and warnings)
These things can be sent to annoy us. Ive had problems using actor references sometimes on begin play and had to delay tick and validate check the actor until it appears valid. Notmally no more than 3 ticks usually.
Anyway, try debugging how i said to start with , then eliminate each possibility