Let's work through this one step at a time.

let's assume the default behavior - and focus specifically on an assignment.

An assignment typically gets an urgency value when it is started; noted above as the "default urgency." 

Then, if, in the SLA, an initial urgency is defined, that value is added to the default urgency as soon as the service level becomes associated with the assignment. 

Given the parameters you note, what would be the urgency value as soon as the assignment starts?

eddie