Tile coords were wrong — Passau at zoom 11 is (1099, 706), not (1102, 710). My earlier hand-calc (1100/706) was close but rounded in the wrong direction. Mosaic 16x16 = 256 tiles took 5-10s to load due to browser 6-connection limit. Reduced to 9x9 = 81 tiles (~2s). Camera already looks down enough that visible ground fits in 9 units.