Whilst a smaller file size isn't an issue, as a recently installed version of avast and little or no changes to the avast default settings wouldn't result in many changes to the avast5.ini.
I honestly don't know what is going on with your avast5.ini file, but I believe that [InetWD] section has to be there, though if no changes are made to the avast defaults it may not be required, but I do find it strange. I have given out this instruction many times and you are the first to report that the [InetWD] section isn't present.
Some changes you can make in the avastUI > Settings > Updates tab:
- Update Parameters, set that to 'My computer is permanently connected to the internet.
- Scroll further down to the Details section and expand that, reduce the 'Auto-update interval to say 180 (3 hours).
- Scroll down to the Proxy Settings (expand that) and change that to 'Direct connection (no proxy).
These change should be reflected in the avast5.ini [InetWD] section.