Mission accomplished! Brain now working properly again.
I have now worked out how to keep it the same size as you zoom in and out:
Using window_matrix.decompose()[2]
to get the 3D View scales to work with. You can still adjust the size using the Size Factor input, currently set to 0.8 in the menu.
I will check all this new code and then upload the new version to my website, I have also added Pivot Point to the operations so it can be set with the Normal, Percent, Intersect & Arc Centre Commands.
Cheers, Clock.
EDIT:
Updated release now on my website.