I put the Enable pin to LOW in the setup() and then tried the above results. I am getting same results as mentioned in the table in the previous long post of mine.
So I dont think its the toggling of the enable pin that is causing the issue.
PS: I am getting a constant hum on the motor now as I have driver is enabled always not to mention the DRV8825 getting warmer because of the constant power draw.
I will try with the mechanical setups today and see if something improves.