If you need higher for your two stacking monitors, you could buy this bundle which include a 31.5 '' long pole (include steel base). Then you could get higher setups! What's more, if your desk thickness is bigger, you could also buy this long pole (with steel base) because this steel base can fit with C-Clamp (for desk thickness up to 3.35" thick) and grommet mount(fits desk thickness up to 1.97" ) In addition, this bundle contains a VESA Adapter Plate Bracket Compatible with Samsung Odyssey G9, Neo G9, CRG9, CHG9 and CHG90 Monitors.
So you do not have to buy it separately.