Differences in size between the individual elements are often used to create a contrast. However, you should pay attention to not force the smaller element into the background.

All elements combined should result in a harmonical image.

It is often helpful to use a grid. For example, an element's width in the logo could be used as the base of such a grid. To achieve a harmonical image, you could use half the width of the first element as the appropriate spacing from other objects or a scripture.

Another example is the logo's "safety clearance", or the space around a logo that should always left blank. Considering a logo that consists of a figure part and a text part (e.g. the SAT 1 logo), you could use the width of the figure part (in this case, the "ball") to define the safety clearance around the entire logo.

Take care when you design a logo with different proportions of the elements: The smaller pat must be easily recognizable or legible also when the logo is used at a small size! Logos should still work down to a size of 2 cm.