I have the function to fill the M event slots with N events (N <= M), the distance between them will be probabilistic correct. For example if you have 20 event slots and 10 events, then the event comes randomly every second slot, but it have small chances to skip several slots or to come every slot.
For 3 elements and 5 slots, for the first element probabilities are:
slot1: 60% (total 60%)
slot2: 30% (total 90%)
slot3: 10% (total 100%; last possible slot)