To which property are you adding Ease In/Out? From your description I can't understand the problem but I will help if I can.
By default a keyframe is Linear, adding Ease converts it to Bezier, with a predefined amount of Ease. You can remove this by Right clicking the keyframe and setting Interpolation to Linear.
For the fine control you want, open the curve editor (the icon with a green and a red line at the top of the Composition panel) and select the property. Click on the keyframe and drag its handles.