I don't understand how cleanplates work

I’ve watched and read tutorials, but when I try to use this technique it seems to me that even if I have use “cleanplates exclusively” ticked Mocha seems to need to have the first and last frame and frames before and after adjusted all the time to get it to create good removal.
Why is this, I thought the idea behind using this tick box was that Mocha would just use the supplied cleanplates and nothing else?
Thanks in advance
Pete B

Hey thanks Martin B
I think I’ve discovered what the problem was. It seems that even though I export the clips using Mocha and touch them up in Photoshop. When I import them in again Mocha names them one frame ahead. I think this might be the setting in the preferences where it says offset frames by 1?
I renamed the frames to match the original frames and it seems to be getting much better results. Still need to add more clips I think as it involves a head turn and I only had two clips for this. One for before the turn and one for just after. I think because Mocha is just blending between the two in a linear fashion I’m getting a few areas where you can see things other than the head. So I’ll try adding some clips and tell you how I get on.
Many thanks
Pete B

Yep this worked fine. Needed the extra frames on the head turn.
Many thanks
Pete B

Hi Pete,
Removal is highly subjective to the content of the footage. Can you send us the footage and mocha files to take a look at?
martinb[at]imagineersystems{dot}com
When you’re using cleanplates exclusively it will try to blend between the clean plates. If there are any lighting changes you may need to set linear or interpolated illumination modelling to help it to look correct.

Hi Pete,
If you want to get the offset next time, you can change that in the Clip tab. By default it can be 1 or 0, so if your frames are labelled differently they can offset.