Which file are you looking at? The "yourproduct.1.0.to.1.1.wyu" file or the "yourproduct.all.to.1.1.wyu" file? The "...all.to...." file contains changed files from the earliest version to the latest version (the full files, not the patches). This is the "catch-all" update that is downloaded by wyUpdate only when a patch fails (i.e. a user modifies your files and the only option is to replace it with the full files).
Tiny Patches not working
Just updated only 1 small file(~500kb) in the new version. The patch size from 1.0 to 1.1 is same as the original ~ 20mb. File/Assembly versions of all the files in 1.1 are same as of 1.0 except the one changed.
Any reason why the incremental patch size is still 20mb?