Cannot descend a specific ramp in transcoast by taking a step back after ascending it

### Describe the bug

There is a ramp in transcoast that you can asend, but that will not let you descend the way you came in.

It's made worse by the fact that there are two turrets waiting at the top.

### Steps to reproduce

1. Load the attached save [transcoast.zip](https://github.com/CleverRaven/Cataclysm-DDA/files/9040018/transcoast.zip)
2. Take two steps west to ascend a ramp
3. See the turrets
4. Take a step east to try to descend
5. Observe that this did not work, and turrets would have shot you now.

### Expected behavior

I expect being able to descend the ramp after ascending it by going in the reverse direction.

### Screenshots

_No response_

### Versions and configuration

- Game version: cdda-linux-tiles-x64-2022-06-30-0619
- Mod list: default

### Additional context

I think the problem might be in the fact that the character ends up on the "Low end" part of the ramp after ascending it (logically he should end up on high end).

Start by loading the attached transcoast.zip save and reproduce the westward ascent followed by the eastward descent attempt. The issue names no source file or test, so trace the ramp movement behavior from this reproduction and verify that reversing direction after ascending allows descent without turret exposure.

Written by the indexing model from the issue text.