Originally, there were settings to set the 'zoom' independently for the 'cube', 'cylinder', and 'sphere' animations. (in Compiz 0.8.8, etc...) This was needed because each scale at wildly different rates.

For example, currently setting the zoom for the cube (say 25%) makes the sphere unusable and makes the cylinder animation too small. Setting the zoom to make the cylinder look right makes the cube to big and the sphere still unusable. Setting the zoom on the sphere properly, makes both the cube and cylinder tiny.

In compiz, there were independent zoom settings for each for this reason. If the hooks still exist for independent settings, it would be a simple task to add the two additional sliders to kcontol > Desktop Behavior > Desktop Effects > Settings > Advanced (tab) (where the current single zoom control is located)

If the independent zoom code wasn't implemented in plasma (or where ever it goes in the current code), it would be worth looking at what it would take to add them. A single zoom setting for all 3 animations is unworkable due to the different scaling requirements.

I didn't know whether this should be a feature request of bug. It is set at bug because there is missing functionality and the current implementation does not work for all 3 animations. Feel free to bump it to a wish-list item if you view it differently. As it sits, you cannot set a zoom that makes all 3 look proper (or even roughly equal in zoom for that matter)

Let me know if you need screenshots. This is fairly self-explanatory. Just set the zoom at different level and look at each of the animations.