Hi DiMenza,
When writing Expository I always think of all my examples as secondary to the main focal point which is your idea.
For instance, you may argue about 'Why Apples are better Than Orange,' you will give reasons, and then examples. This example, might be The Bible (A Text), or it could be McDonalds with their 1 dollar Apple Pie Special, but the examples exist to support and reinforce the reason/idea that you want to prove and argue in that particular program. Another example could be, 'Life Is Worth Living,' one of the reasons could be Life is Worth Living because it brings happiness. You explain that reason, and then introduce an example such as, In the film 'Pride and Prejudice,' we always see Elizabeth incredibly happy, and you link this to why it supports your reason. Therefore, have the mindset that examples exist only to reinforce your main idea in the paragraph and nothing more. This is why, examiners look towards, your primary text example and outside source example. I hope this helps, all the best.
PS: Explain as much as is necessary to prove your point