A solution to get rid of the ganking / counter-ganking with one simple rule and 3 server parameters:
Battles stay open for a minimum time for everyone to join (server setting, maybe t_battle_open_min = 2min). After that, the BR balance is checked. Equal battles (BR1/BR2<BR_max_ratio; BR_max_ratio = 0.7) are closed immediately. Unequal battles stay open only for the side with less BR. Repeat the BR balance check for every ship that joins. Battle is closed regardless of BR ratio after a maximum time (server setting, maybe t_battle_open_max = 10min).
These parameters could be even region dependent (capital zone, safe zone are defined already), but I would not like that, making things too complicated.
Gank fest: set t_battle_open_min=2min and t_battle_open_max=2min and battle will be closed after 2min anyway, BR ratio has no effect.
A bit of ganking: set BR_max_ratio to 0.2 and t_battle_open_max=3min. That means a battles with BR ratio of 1/5 is considered an equal fight and reinforcements have 1min extra time to balance that out.
Eliminate ganking: set t_battle_open_min=1min, BR_max_ratio to 0.9 and extend t_battle_open_max=90min.