Yes, it's true that 1/4 click would be 256 and to get just bigger depths you can multiply that value by how many quarter-clicks are in that depth. So for 1 sector it's 16, and 16*256 is 4096.

I was just trying to explain the formula, that's given for the bridges. Notice that aside from depth you can also specify some other flags, for example if you want to enable hanging from bridge, on top of the calculated depth value (like 4096) you must also add the 64 flag, so you would get 4096 + 64 = 4160. To you this may simply seem like adding two numbers together, but there is a particular reason why the depth value must be multiplied by 256 and can't be represented by the default "game units".

Without going into much detail, if going by the "game units" depth, to get 1/4 click, you would need to enter 64. But 64 Is already reserved for the "Enable hanging" feature. And if you add them, you get 128, which is reserved for "No sliding" feature. So to avoid this, the depth values have this strange calculation.