problems setting #size on select field in views exposed filter form

I have a form_alter hook on views_exposed_form that's trying to adjust how many options are displayed for multiple select fields. Somewhere between that function and theme_select(), though, the "#size" attribute is disappearing. I can set "#attributes" to include a value for 'size', I can add other arbitrary key values to the element like "#test", so I know the form_alter function is being called. I don't see any explicit references to "#size" in core code or in the Better Exposed Filters module that seem like likely culprits. So I guess the whole array is being recreated somewhere?

Looking for ideas on how to find out what's going on here. Thanks.