Oh, I totally understand the need for filtering the number of records returned... I'm just saying that I don't see the need to handle it at the Items property of the Gallery. If you wait until that point to filter your records, you have collected EVERYONE into the DirectReports collection... With 4000 employees under 1 EVP, and how-ever-many EVPs, that's a HUGE number.
I don't know the specifics of the use-cases you are trying to satisfy, but if I were to tackle a generic version of your problem I would ClearCollect() at the point that the manager was selected. That would create a DirectReports collection of ONLY the employees reporting to that Manager, and wouldn't need a Filter.
The caveat to that would be if you want to show ALL the reps under an administrator regardless of filtering it to the Manager (the lowest) level. For example, VP Person1 has 5 Directors, who each have 3 Managers as direct reports, and each of them have 4 Reps. Would you want to pick the VP and show 60 entries? And then, if you picked one of the Directors, you would show 12 entries? And if you picked one of the Managers, you would show 4 entries?
Again, me solving a strawman version of your problem, I would have a Combobox for each level of management (EVP, VP, Director, and Manager). Each would have an Item property pulling from the heirarchy level just above it. Each would, OnChange, Reset() the comboboxes for the heirarchy below them (in effect, blanking them), and then they would rebuild a Collection I would call Reps. The build would have to be smart enough to know how many levels down it needed to drill down until it got to the Rep level (i.e., a Manager would drill one level, a Director would drill two levels, etc.). Then I would have my Gallery set to the Reps collection (no filter required).
Next, I would craft a visual indication of what level we were representing on the form (imagine a color block bounding whatever combobox had established the level of our view - EVP, VP, Director, or Manager. Each combobox, in the OnChange event, would make that bounding box visible and all the others invisible.
Last, I would add a button beside each of the heirarchy comboboxes that would do everything I just mentioned going on in the OnChange event of the combobox EXCEPT for the Reset of the downstream comboboxes. This button would represent us resetting our dashboard view to a particular level without having to make a change to the combobox. For example, you drill from EVP to VP to Director to Manager. You are showing a handful of Reps. You want to back-out to the VP level, so you click on the VP button and the bounding box highlights that combobox as the level being viewed in the dashboard gallery, but leaves the items selected for Director and Manager still selected, should you wish to return to them (by clicking the buttons associated with each).
Make sense? I know sometimes reading about other people's projects can be a little down-in-the-weeds... and this is even worse... this is my down-in-the-weeds about your down-in-the-weeds.