G'day Nino,
I always do the whole backglass for whatever reason, dunno why!
Is there a reason you only touchup a bit?
My thinking is if I do the whole glass it will not deteriorate in the future, from me being careless or from the elements.

The only time I have done a partial backglass was on a Flash. The backglass was absolutely stunning except a small section along the bottom trim. I could not justify doing the entire backglass as it had no other signs of deterioration. As a general rule of thumb, I seal the entire backglass as typically, there are numerous points of deterioration.

I will be using TT on the Buccaneer backglass tomorrow. It has numerous places where there is lift and paint loss. I will seal the glass, then complete some touch ups.