To change the maximum zone size to i.e. 100, replace the lines 299-306 in AddHomeInventoryZoneUI.lua with the text below.

if width > 100 or width < 1 then
self.widthCorrect = false;
widthColor = badColor;
end
if height > 100 or height < 1 then
self.heightCorrect = false;
heightColor = badColor;
end