For some airlines this would not be hard to achieve on certain routes. I regularly fly from HKG to the USA, Europe and AUS. Almost every time we are in a cluster of other company aircraft. It is not unusual to have 5+ company aircraft within 100 miles of each other on the same airway. On 8-15+ hr flights it would not take up a huge amount of time to close gaps between adjacent pairs. If you have doubts look at flight radar24 at 1800z at the line of CX aircraft heading to Europe and also the USA.