You can achieve better compression ratios resulting in significantly smaller file sizes by pre-compressing files as part of the deployment process. That’s because brotli compression can be somewhat resource intensive, so edge computing tends to dial back the amount of compression to compensate.
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Options for Brotli Compression Using Cloudfront and S3
When using AWS S3 as an origin to serve a static website distributed by AWS Cloudfront you need to choose how to enable brotli compression. These choices are mutually exclusive—you can either a) have Cloudfront compress to brotli at the edge with a 20% ratio with fallbacks for gzip or no compression or b) compress to brotli by pre-compressing assets where you can use a much higher ratio (80%), but with no fallbacks.