Treat the corner preference as useful information
A cat who returns to one particular corner for every toilet visit is not being stubborn for amusement; she has weighed safety, quiet, footing, scent, and escape routes and found the spot that passes every test. That corner may face the room so she cannot be surprised, sit far from food and noisy appliances, or simply hold a surface and smell she trusts. Working with that verdict is far easier than retraining it, so make the preferred corner the site of your best tray: the roomiest box, the litter she digs in happily, and the depth she leaves covered neatly. Arguing with a working preference by placing the tray where it looks tidier to humans usually buys you deposits in the corner anyway, without a tray under them.
Protect the favorite from competition
The complication in a multi-cat home is that the perfect corner is visible to everyone, and a second cat who also likes it, guards it, or simply soils it first can push the devoted cat into a miserable choice. Keep the total at one tray per cat plus one extra, place the other trays in genuinely different areas rather than lining them up beside the favorite, and scoop the preferred corner first on every round so it is almost always ready for its loyal user. If you see waiting, hovering, or a cat leaving the corner tray unburied and hurrying away, that location has become contested, so add distance between options rather than a bigger box in the same contested spot.
Keep everything about that corner boringly consistent
Preference this strong is usually built on details, so change one thing at a time and never several at once. Keep the same unscented litter, the same fill depth, and the same open or covered style; when you wash the tray, a mild rinse that leaves it clean but not strongly perfumed preserves the familiar background scent that tells her this is still her place. Do not rearrange furniture near the corner, store the vacuum there, or let children play directly beside it, because each change chips away at the calm that created the preference. If you must switch litter, blend the new kind in gradually in a second tray first and watch which one she chooses before touching the favorite.
When a sudden corner fixation is a warning
A long-standing preference is normal, but a cat who abruptly abandons all trays for one new corner, or who starts toileting in a corner without any tray, deserves a closer look. Pain, urgency, or a tray that has become hard to enter can all present as a new location habit, and straining, small frequent deposits, crying, or blood in the urine mean a prompt veterinary call rather than another box experiment. Also check the practical story: a recently moved tray, a new pet blocking the old route, a guest in the room that housed a tray, or a litter change in the same week often explains a sudden shift that looks mysterious until the timeline is written down.
Making sure helpers respect the winning corner
The favorite tray is the one most at risk from a well-meaning helper who tidies it into a different spot or swaps its litter for whatever was on offer, so record its exact corner, box, and litter in the household routine. Noting that preference in KinsLe Care Teams means anyone assigned to scoop sees that this corner tray stays exactly as its devoted cat likes it, with its completed cleans marked for the next person.