With this tool, you can resize the red rectangle thing, easily.
It is an abstraction, so you put it in your abstractions folder (Pd path). In fact, there are two files: redsize.pd and redsize_abs.pd.
Activate graph on parent, (if you haven't done it yet).
Call redsize into your subpatch, abstraction, or whatever, by typing redsize into an object box.
You are going to see this:
Open it, and there you´ll find all necessary controls and simple instructions. Basically, you'll control the red rectangle from a small window.
Notice that it's a variation on the work done by @sensn who generously shared it 3 months ago here: http://forum.pdpatchrepo.info/topic/8590/graph-on-parent-box/
Also, his recent comments have made me correct a few bugs! Thank you sensn.