The US delegation concurs (well, I do anyway...). They're too close when they get too close, not when they're as HD has characterized this situation...
one aircraft is climbing thru' 14000 and another a/c, which is considerably slower, is climbing thru' 6000 and they are on diverging tracks. So, by the time they both reach 17000 they will be many miles apart, with the distance rapidly increasing.
They pay us to use our brains in exactly this manner. To fail to anticipate this sep would trouble me. Of course, stranger problems have developed, but that's why we continue to watch these things...
Dave