Can I set the volume on my iPhone lower than the slider goes?
There's a very simple solution for your problem. Go to 'settings' > 'Music' > Volume Limit. There you can limit the maximum volume. How lower the maximum volume, how smaller the increased or decreased volume difference when you click on the volume rocker.
What is fixed position volume control?
Go to Settings > Sounds. Turn on Fixed Position Volume Controls if you want the volume buttons to always have the same behavior. Turn it off if you want the volume buttons to change dynamically depending on the orientation of your iPad.