As written in the php doc, this is the list of ids of the items that shall be made available for option retrival.
See: https://github.com/MetaModels/core/blob/dev/src/system/modules/metamodels/IMetaModelFilterSetting.php#L85

This is needed to limit the options to the "remaining items" when having multiple filters (select A, select B) and one of those is active (select A) and the current filter (select B) shall only show the options still available after filtering away anything that is not matched by the first one.
You are effectively killing this functionality by passing null here, aren't you? :)
Therefore, we need to elaborate what the "weird results" are a little more.
I see the fact that the array was not being used before, but IMO the functionality will be needed using your new min/max values as the limiting will affect minimum and maximum as non matching items might reduce the spanning of valid min/max values.