Before I go any further, and so there's no misunderstanding, I'm not saying that what you've done is wrong. Only that by not fully understanding the principles of design, the way people see and perceive the image is highly dependant on the environment in which they view it. The image changes depending on the background it's viewed against.
I like to try and show you this, explain why it is, and how to remove the confusion because I see a lot of this and I'm not sure it's fully understood by photographers.
What I'm talking about is not utilising the range of tones available and how this affects the way the image is seen. Here's a threshold map of the 4th image showing the brightest two pixels at 143, (the colour histogram shows the red channel as having brighter pixels but on an RGB screen with no green or blue present this still only represents half the brightness possible).
So how does this affect the way the image is seen sand percieved? For this little experiment in vision and how we see you will need to download the 4 images and open them in your image viewer, with the images at 100% and the viewer set to 'full screen' with a black background. The idea is that you view each image against a full black background.
Now if you open
original_black_ground.jpg so you view it against a full screen black background and view it for 30 seconds or more, to let the eye adjust, and you will see a near full range of tones, colour and contrast. The key point here is;
let the eye adjust.
Now if you flick the image to
original_white_ground.jpg see how the impression of tone, colour and contrast changes. If you view this image for 30 seconds you will see that this impression is maintained.
So what's happening here? The key point is that the
eye adjusts. We don't see in absolute values only relative ones, we don't see that x is at a certain luminance only that it is brighter/darker than y. You brain then adjusts this information to try and see a full range of tones between these points, just like an 'auto levels' adjustment. What happens when you present the image on a white ground is that you give the eye a much brighter tone as a reference and it now sees the other tones as occupying only half the range of tones between the black and the 'new' white. We now see the tones and colours relative to the white ground and not the brightest tone in the image.
My edits are in no way presented as correct, but if you flick between them you'll see that the perception of tone, colour and contrast is far more stable simply because I've included the reference points with the image, so the background or border is far less critical.
There is nothing wrong with only using the lower half the tones available, but if you want the viewer to see it as dark then you must include the reference bright point (as simple as a white border) or the viewer's perception of tone, colour, and contrast will vary depending on the background against which it's viewed.