What behavior do you want with your “Help” point?
Only one variable per coordinate can change. So, if your expectation is that the graph change similar to what occurs with the green point, it won’t work this way. In “Help”, each coordinate uses a and q and only one variable can change, while the green point only uses q for the x-coordinate and a in the y-coordinate.
You can fix particular variables by making an expression or fraction. So, if you want p to be fixed for example, you can define it as p=1/1 and the slider will be removed.
You can also explicitly define the parts you don’t want to affect the movement. Like if you only wanted to adjust your point based on q, you can explicitly define the radical. Below has the original non-draggable point, and an edited point that will adjust based on q:
