I don't know if this is still relevant, but I made a well earlier by channeling down ten or so levels to an open space that descended a few levels before actually getting to the top of 7/7 water underground. What I told my miner to dig basically looked like this, where # is a wall tile to be mined out, _ is a channel to be dug, O is open space, and W is water, from the side:
############_
_
_
_
_
_
_
_
O
O
O
W
So my miner goes and happily mines out the walls as normal, gets to the channel, and yes, digs a ramp. He digs a ramp down the next level too, and down the next, and so on. I thought, "Curious," and left to go do something else. When I came back, Urist had smashed into the water below, blood splashing everywhere, and eventually drowned. On the plus side, all of the ramps had disappeared and in their place was the traditional open space expected from a channel. So instead of V I had _, if you know what I mean, *nudgenudgewinkwink.*
So the whole process does indeed make channels, and it just looks like the ramps are there for an extremely temporary conven- Or on second thought once Urist broke through the bottom layer to the open space eight levels of ramps may very well have fallen and smashed into his broken body and pinning him under seven levels of water until he drowned.
I'm not sure, all I know is I have nice channels for my well instead of silly ramps, and that I didn't need to dig access tunnels for the channels. All for the price of my only other pick and a novice miner.
Carry on.