Indeed a very interesting question, here are some thoughts:
Problem is that there is little known about the wreck site. What do we know more then Ken Marschall's painting and some fuzzy wreck pictures?
Anyway, I assume that the 400m figure is for the funnel which is the one most far away from this wreck, so the other 2 funnels are between #1 and this one.(#1 is next to the wreck). 4 funnels in 400 meters is not a really large area.(the ship itself is 270 m!)
So I think it's quite important to see the 400 meters in comparison with the other important sizes.
The ship is about 270 meters, the depth of the wreck is 110 meters and a funnel itself is, IIRC, around the 18/19 meters.
110 meters is quite a drop, but it's not a solid object. It's quite large in size, but it's weight is relativily low. I can image that it drifts/moves in it's downfall to the bottom, it will not fall down like a rock. And the (slow)forward momentum of the ship and a current can/will do this.
So, I have to agree with Rev. Fleming, who says the funnels 'melt like wax and crash onto the decks one by one' before the ship 'leaves hardly a ripple behind'.
The aft 3 funnels fall off one by one, the ship travels about 1x it's lenght from the moment the first one falls off, and then hits the bottom and sinks.
It wouldn't have to do much with Bartlett's beaching attempts, 400 meters isn't far, and when I would have been captain, a funnel crashing onto the deck would *not* be a good sign...(certainly not when you think this deck is full with lifeboats/liferafts and perhaps people. If it happened when the ship had still people/nurses onboard, some reports would have existed of falling funnels causing panic, damage, casualties etc.)
Hope this all makes some sense!
Comments are very welcome.
Regards,
Remco