The point about joining the tanker in echelon means that you can come steaming in and then put the speedbrakes out whilst, as you pull level with the flight deck, announcing you've finally arrived from 70 miles away. Useful in EMCON silent conditions.
Surely you do have to be more circumspect when joining directly astern.
I remember during GW1 on a night towline in NW Saudi, a US Navy S-3 Viking had joined astern, plugged in and started taking fuel before the Eng had noticed. Had he joined on the left and moved abeam the flight deck, I would suggest it would have been safer.