I will paste the details about the mentioned private support thread here so that other members of the community have enough information to evaluate the request:
In order to change the height of the list, we use [listHeight] option. By default the option is set to 200px. I prepared an example to demonstrate the above suggestions:
You can change the size of the Popup via the popupSettings height and width options:
... but changing the dimensions via user interaction (dragging a part of the Popup) is not supported.
Setting the height of both the list of options and their Popup container is already available via the options described above.
If this request is about a functionality that will allow the end user to resize the Popup via dragging its corners, please let us know so we can adjust the request accordingly.
Dimiter TopalovProgress Telerik