SKNodes with SKPhysicsBody under SKAction move inaccuracy - objective-c

Question

I have two SKNode with physics (one under another):
- (SKNode*) newNode {
SKShapeNode *node = [SKShapeNode shapeNodeWithCircleOfRadius:60];
node.strokeColor = [SKColor clearColor];
node.fillColor = [SKColor greenColor];
node.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:60];
node.physicsBody.categoryBitMask = 1;
node.physicsBody.collisionBitMask = 1;
node.physicsBody.contactTestBitMask = 1;
return node;
}
- (void)createSceneContents {
SKNode *n1 = [self newNode];
n1.position = CGPointMake(100,100);
[self addChild:n1];
SKNode *n2 = [self newNode];
n2.position = CGPointMake(100,300);
[self addChild:n2];
...
}
Their goal is to reach a predetermined position directly opposite them at some distance.
To achieve this, I use SKAction (this is important and can not be changed):
[n1 runAction:[SKAction moveTo:CGPointMake(800,100) duration:3]];
[n2 runAction:[SKAction moveTo:CGPointMake(800,300) duration:3]];
In addition, on the first node's movement path I place a third node - exactly the same.
- (void)createSceneContents {
...
SKNode *obstacle = [self newNode];
obstacle = CGPointMake(500,300);
[self addChild:obstacle];
}
The third node must be shifted in the direction of first node's movement by the mechanism of physics.
Click to illustration of the Scene
(the red circles marks destination position of nodes)
Then I run the app, everything goes as is conceived, except for one thing - a first node (with obstacle on the path) was not reach the target location, just a few pixels:
Click to see result
The question is simple: why? And how can I fix it?
Thank you!