When a cat scratches one sofa corner, a cat scratch mat or post across the room may be too far from the familiar target. Start with placement: put an appropriate scratching surface close to the exact spot, then make it stable and easy for your cat to approach.
Quick take: Begin beside the scratched arm or corner, observe the cat’s preferred angle, and move the post gradually only if the cat uses it consistently.
Start beside the exact sofa area

Identify whether the cat reaches for the arm, outer side, or front corner of the sofa. Put the scratching post or mat right beside that area, with enough room for the cat to stand and stretch. The ASPCA recommends placing posts near objects the cat is inclined to scratch and offering attractive alternatives.
If the furniture is in a busy room, do not hide the post behind a door or in a spot the cat rarely visits. Keep the approach clear and avoid a location where the base can be kicked or knocked over.
Make the post comfortable to use

Check that the base sits flat and the post does not wobble when you press it gently. A vertical post should allow your cat to reach upward; a horizontal mat should stay flat rather than curling. The ASPCA notes that many cats prefer a sturdy post that will not shift and one tall enough for a full stretch.
Try a vertical cat scratching post first if the cat reaches up the sofa arm. Try a horizontal cardboard scratcher (paid link to Amazon) if the target is low or the cat scratches the floor-level edge. A sisal scratching post and a cardboard pad offer different textures, so use the cat’s choices to guide you.
Protect the sofa while you test placement

Cover the targeted sofa area only with a material compatible with its upholstery, and keep the post next to the protected spot. Do not force the cat’s paws onto the post; let it investigate voluntarily. If it does not use the first setup, change one detail at a time—height, angle, material, or position—so you can tell what helped.
For the broader room plan, read the cat-friendly furniture protection guide. If the post still moves, see how to choose a stable scratching post.
Try this today
Put a stable scratcher beside the sofa area your cat already uses, leaving enough room for a full stretch and a clear walking path. Watch for voluntary use over several days and adjust the position if your cat keeps returning to the sofa.
Keep reading: cat-friendly furniture protection guide; compare vertical and horizontal scratchers; choose a stable post
Helpful sources
Optional horizontal scratcher to compare
The PetFusion Jumbo Cat Scratcher Lounge may suit a cat that already chooses a low, horizontal cardboard surface beside a sofa. Check the listed footprint (about 99 × 28 cm) against the available floor space; it is a large lounge rather than a compact upright post. Observe whether your cat uses the surface before changing the placement plan.
View the PetFusion cat scratcher lounge on Amazon (paid link)
As an Amazon Associate I earn from qualifying purchases.