Welcome to the TP Support Site.
What you are trying to do is not possible at this time if you are working with just the Article Layout for the FrontPage. You are limited to those 4 options. However, theoretically, if you place each of your articles into a "Single Article" type block, and take advantage of the panel settings, you could do this but it might take a little bit of work.
For instance, let's say that you have 16 articles, and we will number them 01 to 16, and you want to show them on the FrontPage only. If you look under the Panel settings under TPAdmin and scroll down to the Front Panel, you can "Display the blocks in 4 columns" and "Force this width on each block(use 00px or 00%):" to be 25%, each of those Single Article blocks will show up in the FrontPanel and be populated as follows ...
|Article01 Article02 Article03 Article04|
Article05 Article06 Article07 Article08
Article09 Article10 Article11 Article12
Article13 Article14 Article15 Article16
It also might look better if you "Force this heigth on each block(use 00px or 00%):" to a particular height as well so that the look of the blocks will be uniform. This is pretty much going to require all of your Articles to have the same basic look so that you don't generate horizontal scroll bars in any one block.
You can get a rough idea of what this might look like by taking a look at the Forum BoardIndex on my test Forum ~ http://talesofthehavenexpanse.com/smf2test/index.php?action=forum
If you look at that page, you can see that I have setup a left panel (top block is the Welcome block) and a right panel (top block i is the User block). Between those 2 panels, I have another User block, a shout Block, and a Stats block. Those 3 in the middle are all in the upper panel and that panel is set to display in 3 columns and each block is set to force the width and height of each to a particular value. This could just as well be set to 4 columns and each block could be a "Single Article" block.
In the next version of TinyPortal, bloc is working on a new feature which might make what you are trying to do somewhat easier. Does this give you some ideas to try?
Edit: Ah, Ichbin posted while I was thinking about this. What he has said is correct though. Most of your members would not get a good view of what's really on your FrontPage if you splashed 4 Articles across the page like that. The content of each Article would have to be very narrow.
What you need to keep in mind is that the most popular screen resolution is still 1024 X 768. I use 1280 X 800 and I wouldn't even want to try 4 columns, even if everybody viewing my site is using that screen resolution.