Position watermark
When you first create this watermark, it is automatically assigned a random position attribute. If you wish to show it always at the bottom-right corner, all you need to do is (while the watermark is selected) to click the position icon in the Watermark editor. The position icons are 9 squares and can be found easily. You can only have one of the nine positions so if you choose another one, the previous position icon will turn into hollow. A solid icon indicates the current position of the selected watermark. If you do not want auto position, you can click the solid icon again to make is hollow. In this case, you are using absolute watermark position which means you may miss the watermark on another picture of smaller size because it is outside the bound of the smaller image.
Size watermark
Watermark size can also be absolute or relative. Relative size covers a consistent percentage of your image size. Both have advantages and disadvantages. This should be your choice. By default, 50% relative size is used when you create the first watermark. If you change the font size, it will turn into absolute size.