The defensive support sector bonus is based on the support pool of the guild, and it's identical for all maps. The pool, however, is divided by a factor for each map, so it covers fewer and fewer sectors, and it's then distributed +75 to the HQ, then +50 to "nearby" sectors, in groups of six. The lower zones have lower caps.
The offensive bonus is player by player. Note that the "Attack Bonus" also includes a defensive bonus that allows the attacking troops to absorb more hits before they die. A high attack bonus means the the fights will be shorter, and that your troops will take less damage, so as your attack bonus gets higher and higher it's more and more likely that your troops will be injured, rather than killed.
The sector defensive bonus is recalculated once per day, and has nothing to do with who placed the garrison armies nor with who captured the sector.