1. Ensure that the you have accepted all of your suggested terms you deem related to the topic:

When you click suggested terms (blue boxes) and turn them into accepted terms (green boxes) inside a topic. Those green terms define the topic. The scores are calculated when some special "sentimental" word is directed towards the topic – which was determined by the terms. Thus, having a wider coverage for your topic because of the extra terms then will probably have more sentimental words directed at the topic. Which could increases your sentimental text counts.

2. Sentiment Scores are determined by sentiment pointing at the topics. So the data just might not have topics with a lot of sentiment pointing towards the topic. Which could seem misleading about certain topic's sentiment score but there just might not be sentimental texts.

3. The survey question you are asking could be priming the users to not use sentimental texts. For example, the difference between asking about: 

1. Did you like the colour? - tends to lead towards yes or no and very unemotional text

2. What are your thoughts on the colour? - tends to lead towards open ended and emotional text