soaringhigh650:
Size of Target: Depends on whether it is displayed on an old analogue screen (circular, with rotating sweep, primary radar only, like the now obsolete Marconi 264S) - in this case the radar blip will vary in size, being larger at the edge of the screen and getting smaller as it approaches the center. Most radars in use today have digital screens where the targets are synthetically generated and displayed on the screen. They all thus appear at the same size on the screen - though there are normally a range of sizes that the controller can set (for ease of reading the target labels). The so-called 'blips' on modern radar screens are processed into different shapes according to how the radar information was obtained: from primary radar only, from secondary radar only, or from both primary and secondary radars. The controller can thus readily determine from where an aircraft's radar return came.
The controllers job is to see that they do not let their 'controlled' targets get closer than the minimum separation (either lateral or vertical) distances. The targets can pass over each other if vertical separation exists.