Seriously? How many minutes apart do you think 10 miles represents at 30 miles? 2 - 2.5 minutes is the correct answer. The actual distance is immaterial (aside from maintaining a radar standard), it's how much time it represents that counts because that's the time spacing onto the runway.
How long does it take you from crossing the fence to vacating the runway? What about when there aren't adequate high speed exits?
I do arrivals into ML & if I hand off a domestic behind an International heavy with much less than 12 miles there won't be 5 miles on final without intervention.