Screen Mode

Muffed supports 2 different screen modes for multiplayer rendering. The first is Shared Mode. While in Shared Mode all players will appear on the same viewport, which will automatically zoom in and out based on players' positions. The second is Split Mode. While in Split Mode each player will get their own viewport, which can be manually zoomed in and out via the player's input.
[Options > Graphics > Multiplayer Render Options > Screen Mode]

Shared Screen Padding

While in Shared Mode this option will determine the amount of padding that the players get around them before the viewport begins to zoom. Setting a lower value will result in a closer default zoom but less visiblity. Setting a higher value will have the opposite result.
[Options > Graphics > Multiplayer Render Options > Shared Screen Options]

Split Screen Mode

Split Mode has 2 different versions. The first is Full Utilization. While in Full Utilization mode the game will use all available pixels in the game window to create viewports, even if one or more players get larger or smaller viewports than others. For example, when running the game at a 1920x1080 resolution and with 5 players, two of those players would get 25% of the screen each while the other three players would each only get 16.66% - one third of the bottom half of the screen.

The second is Identical Viewports. While in Identical Viewports mode the game will force each player to get an identical viewport size. This will often result in there being a large un-used portion of the game window.
[Options > Graphics > Multiplayer Render Options > Split Screen Options]

Split Screen Spacing

While in Split Mode the pixel-width of the black space between each viewport can be altered. Setting this to 0 would result in each viewport being right next to each other, but can often cause confusion concerning where a player's viewport ends.
[Options > Graphics > Multiplayer Render Options > Split Screen Options]

Split Screen Sizes

Muffed will divide up the available game window into sections and make each viewport as square as possible, while still using the full game window space. This is why you may see the game split in different ways, depending on aspect ratio. For example, when running the game at 1920x1080 with 3 players, the screen will be split vertically. However, when running the game at 1080x1920 (vertical 1080p monitor) the screen will be split horizontally. Using this information, you could do something like run the game spanned on 3 monitors, to ensure that each player would get their own monitor (assuming the spanning was occuring in a line, all at the same orientation and resolution).