After R1 2019 Telerik Web Report Viewers use Kendo splitter for resizing Parameters and Document map areas. At this point, there is no way to change the Parameters Areas position.
When using the Report Viewer under WinForms, Print Preview allows the user to scroll through all report documents. I.E., everything in the document map. However, when using the Wpf version you cannot. In the Wpf version, the user must use the Document map to select and scroll through each particular area. For large reports containing multiple documents, this is tedious. Please make the Print Preview functionality for the WPF control match that supported by the WinForms control.
I had compare crystal report and Telerik report on rendering similar dataset. (LARGE dataset) Crystal report renders much faster on showing the initial page (viewer) by almost 50% compare to Telerik html5 viewer. (almost 10,000 pages) Crystal report renders much faster on generating PDF file by also 50%. Also Crystal report telling the total page on the initial rendered page., while on Telerik report (html5 viewer) it on shows pages that are already cache (and show caching progress.) It would be nice if it show the total pages then shows in the status notification the progress of caching.