Is there relationship between model and form of base graph?

Hi, I'm interested in your novel work.
I tried to change some condition in 'demo/physics.ipynb'.
I wonder whether it also predict velocity well when I change initial position of spring.
For example, I changed that the only first mass is fixed in function 'base_graph'.(it means the last mass is not fixed.)
And I added damping force with hooke's law in Springsimulator.
I thought this is so small condition for affecting but, the result of inference didn't follow target and spread out.

Is there relationship between model structure and form of initial condition(such as base graph)?
and how can I change it to fit the target?