Sharp lines in corners of Threejs BoxGeometry shadows

I made a structure using BoxGeometry, and I have a DirectionalLight rotating around it. The problem is, I can see aliased light bleed in the corners. I’ve tried updating the shadow.mapSize, the blur radius, the renderer.shadowMap.type, but nothing has worked so far.

//left wall
const geometry = new THREE.BoxGeometry( 1, 15, 7 );
const material = new THREE.MeshPhongMaterial( {color: 0xFFFFFF} );
const cube = new THREE.Mesh( geometry, material );
cube.position.y = 7.5; 
cube.position.z = -4.5; 
cube.receiveShadow = true
cube.castShadow = true
scene.add( cube );

//right wall
const geometry2 = new THREE.BoxGeometry( 1, 15, 7 );
const material2 = new THREE.MeshPhongMaterial( {color: 0xFFFFFF} );
const cube2 = new THREE.Mesh( geometry2, material2);
cube2.position.y = 7.5;
cube2.position.z = -4.5; 
cube2.position.x = 16; 
cube2.receiveShadow = true
cube2.castShadow = true
scene.add( cube2 );


//back wall
const geometry3 = new THREE.BoxGeometry( 1, 15, 15 );
const material3 = new THREE.MeshPhongMaterial( {color: 0xFFFFFF} );
const cube3 = new THREE.Mesh( geometry3, material3);
cube3.position.y = 7.5;
cube3.position.x = 8;
cube3.position.z = -7.5 
cube3.rotateY(Math.PI / 2)
cube3.receiveShadow = true
cube3.castShadow = true
scene.add( cube3 );


//top
const geometry4 = new THREE.BoxGeometry( 1, 7, 17 );
const material4 = new THREE.MeshPhongMaterial( {color: 0xFFFFFF} );
const cube4 = new THREE.Mesh( geometry4, material4);
cube4.position.y = 15.5;
cube4.position.x = 8;
cube4.position.z = -4.5 
cube4.rotateY(Math.PI / 2)
cube4.rotateZ(Math.PI / 2)
cube4.receiveShadow = true
cube4.castShadow = true
scene.add( cube4 );




// DIRECTIONAL LIGHT
const directionalLight = new THREE.DirectionalLight(0xffffff, 1);
directionalLight.position.x += 20
directionalLight.position.y += 20
directionalLight.position.z += 20
directionalLight.castShadow = true
directionalLight.shadow.mapSize.width = settings.shadowMapSize;
directionalLight.shadow.mapSize.height = settings.shadowMapSize;
directionalLight.shadow.radius = settings.shadowRadius
// directionalLight.shadow.blurSamples = 500
const d = 25;
directionalLight.shadow.camera.near = 0.5
directionalLight.shadow.camera.far = 60
directionalLight.shadow.camera.left = - d;
directionalLight.shadow.camera.right = d;
directionalLight.shadow.camera.top = d;
directionalLight.shadow.camera.bottom = - d;
scene.add(directionalLight);

scene.add( new THREE.CameraHelper( directionalLight.shadow.camera ) );