fastSLAM performance

[theColorfulRainbow]

Hello, Really cool project :) Got a question regarding the performance. I played around with changing the position of the landmarks. I mainly noticed that the fewer Landmarks there are, the worse the performance gets. Also, was wondering why the performance of the algorithm is very bad when I only make the robot move forward. I can give a more in-depth explanation with example if you'd like. Regards.

Example of robot moving forward