The expedition location will usually spawn within 10 jumps from the system where you received it. So to hopefully get the escalation in high sec systems you’ll have to make sure you’re over 10 jumps away from low sec systems.
About a week or 2 ago I jumped into Rens system and saw Angel Refuge anomaly on scan, warped in, completed it and got escalation to DED 5/10 Angel Red Light District. The Agency showed it to be 9 jumps away and after setting destination the route showed it to be 14 jumps away.
The reason for that is because I have Autopilot settings for safer route - stay in high sec systems. The location could have easily been in low sec so that was pure RNG luck. However the expedition location itself was in Amarr high sec system so that means the expedition doesn’t have to spawn within the same Region. Now if I hadn’t had positive standings with Amarr, that expedition would have been worse than having it spawn in low sec system.
Sooo, the main thing to remember is the expedition site location can spawn anywhere within 10 jumps from the system where it was initially gained.