Star Wars for Electives is ultimately, meant to serve the seniors first.
Those schools which has earlier registration date obviously gets first priority in that queue.
First few school to register seniors gets allocated first. Then juniors. Next day another school register. Seniors will push back the first course juniors in terms of allocation.
So its pretty simple, look at the waitlist everyday until your registration date arrived. If vacancy > waitlist. You are somewhat safe. If not, try your luck.
Dont be so stupiak and put your choice as number 1 when vacancy <<< waitlist.
And another thing is, the system for "Waitlist" doesnt mention the ranking of UE.
Or alternatively, wait till ADD/DROP. The system eventually will reach its point of equilibrium where students will drop courses and you cn get your vacancies.
If not, too bad. Learn to email the coordinator of the course, not the prof.