In H1 and H2, encounters are set up to challenge a group of 5 characters of the encounter level (EL), which equates to 500/625/750/875/1,000 XP for ELs 1/2/3/4/5. Since I'll have 9 characters in the group, encounters will have their experience budget adjusted by x1.8, so the XP budgets are:
900(+400) / 1,125(+500) / 1,350(+600) / 1,575(+700) / 1,800(+800)
In general, encounters will be boosted by adding in more of existing creatures at approximately the ratios they are already present in. Additional creatures XP value should add up to the "+" numbers listed above. Unique creatures will not be added to in this fashion. If they have followers or minions, they will be increased in numbers to compensate. If not, or if no suitable creatures are in the encounter to be added, the unique creatures may be "bumped" in level to a maximum of 3 levels above the party level.