Index.html

Does adding index.html at a new directory depth level help indexing all of that level?

No it makes virtually no difference.

You have to be careful of this because of something called the directory index.

When you type

domain.com/directory
and
domain.com/directory/

They are actually different things. Technically the first URL there is looking at the top levelf for a file called directory not an actual directory. The second is looking for a directory but specifying no file.

The Directory Index auto appends this to a common file set at server config. For most practical purposes this is index.html (and often a cascade of index.php etc etc is operated).
On a Lotus Domino Server the directory index is default.html by default.

You just need to be aware of issues such as this so you know what you have.

IMO it is always best to put the full absolute URL then there can be no config issues so to that end putting the index.html part is benneficial.

Ok thanks for your help. I will use the absolute URL's.