How can the amount of data in a sampled google analytics report be increased?

Under the reporting interface of google analytics. The reporting tool base the amount of sample on the precision setting of the report. Greater precision will need more sample and less precision setting will need less sample. It is the percent of N session which is changed depending on the setting. You can find more information and official documentation on Google analytics product page.

Greater precision option will provide max sample.

answer; geometric center line;