What do the following settings mean in a sequential download options dialogue box-

1. Minimum Seed count
2. Aggressive Percent
3. Progress Limit Percent
4. File Tail MB
File tail percent

1.) Minimum Seed count
If there are less than # amount of seeders, Tixati won't download sequentially.
2.) Agressive Percent
How much should Tixati enforce the sequential download setting. Generally the Bittorrent protocol works better if the peers prioritize downloading the rarest pieces first.
3.) Progress Limit Percent
Stop downloading sequentially after the download reaches # percent.
4.) File Tail MB
There are many files (example some video formats, pdf) that store metadata at the end.
Because of this, sequential downloading starts at the beginning and at the end of the file, essentially giving you the option to start viewing it before the whole download finished.
If your main downloads are wav files, it can be set to 0 MB, while HD video files may need 10-20 MB of tail for the last frames.
5.) File tail percent
Same as File Tail MB, except the size is specified in percent. If the file Tail MB is not applicable (ex. being bigger than the file size) use % based calculation.

2. and 3. are guesses, I'm not sure about them.