App Downloading at a Different Size than App Store says
For some time now, iOS automatically clears app caches when your iPhone storage approaches full.



For this reason, there is little need to interfere by cleaning the caches manually. However, if you still want to clear the caches yourself, there are apps on the App Store that offer this functionality. 'Battery Doctor' (free) is one example - it offers many maintenance tools, including the option to delete 'junk data' from your phone