Whatever your analytics say about desktop conversion, the first visit to a 3D web experience very often happens on a phone — from a chat link, on a commute, with one thumb available. That six-inch window deserves first-class design, not a squeezed-down desktop HUD.
Three problems dominate. Occlusion: fingers cover the screen they control, so persistent controls must live at the edges — Holovate docks an explicit D-pad at the bottom of the world view rather than floating a joystick over the scenery. Density: a desktop HUD's six stat tiles become two columns; anything that cannot earn its pixels at that size moves below the fold. Gesture conflict: the browser owns swipe and pinch in ways an embedded canvas must negotiate carefully, which is why drag-to-orbit happens inside the canvas and page scrolling stays outside it.
Readability is the quiet fourth problem. Text over a live 3D scene needs a backing panel with blur and real contrast at 375 pixels wide — atmospheric typography that works on a monitor becomes noise on glass in sunlight.
Design for the six-inch window first and the desktop version inherits discipline for free. The reverse almost never works.
Open the world on your phone and you will see every one of these choices in place.