Hello aviva,
Thank you for detailing your concern, my apologies for the delay of this reply. Object bonus is controlled my the estate owner. Residents with parcels on the mainland can take advantage of any object bonus, however, they do not have any control over the region management of the bonus level.
Mainland locations with object bonus are special locations, primarily in the themed parcel areas like, Bay City, Nautilus, Horizons, and some Zindra locations.
As a mainland land owner, you only have access to the settings that are available in the About Land information of your land. You will not be able to manage object bonus on the mainland, this is only an option on private estates, along with total control of the estate tools.
I hope this answers your questions, let me know if I can try to help further.
Sincerely,