Drillerman, that's correct. Since the ship is relatively long and thin, placing dots at each corner of the image canvas will trick the game into thinking the ship is square. Since there are lots of transparent pixels between these dots and the ship, the ship will appear smaller in-game.
However, if you try this with the Death Star, the effect will be less noticeable, since the shape of it already fills most of the image. This is case is even more extreme with a Borg Cube, which fills almost all the image canvas.
What you will also find is that the triangle around the ship will increase in size, since the game thinks those transparent pixels around it are part of the ship, but we can't see those parts.
There are 2 key rules to account for when considering how large a ship will render.
1. The game renders ships on-screen based on the transparent to opaque pixel ratio. This results in long-slender designs being rendered larger, and square-chubby designs looks smaller, unless the ship has a large hole in the middle, thus making it have more transparent pixels. This is by design so as to represent the correct size of ship for it's surface area.
2. The game will always ignore all the transparent pixels around the edge of your image box. It will cut to the point where the first opaque pixels are found. So making an image 500x500 and placing a 250x250 ship inside it, will result in the game cutting the redundant transparent pixels. That's where Tyrador's example of adding pixels to each corner comes in useful for reducing the ships render size.
I haven't found any way to increase a ship's size without changing the shape of the ship. A Borg Cube must remain a square for example, but I can tilt it on it's side slightly to give it some more transparent pixels, thus increasing it marginally.