Dodgy collision detection

private void HandleCollisions()
        {
            var gridX = Mathf.Floor(_player.x / TileWidth);
            var gridY = Mathf.Floor(_player.y / TileHeight);

            for (var x = gridX - 1; x <= gridX + 1; x++)
            {
                for (var y = gridY - 1; y <= gridY + 1; y++)
                {
                    if (_tiles[(int)x, (int)y] != null)
                    {
                        var tile = _tiles[(int)x, (int)y];
                        var tileRect = tile.localRect.CloneAndOffset(tile.x, tile.y);
                        var playerRect = _player.localRect.CloneAndOffset(_player.x, _player.y);

                        if (tileRect.CheckIntersect(playerRect))
                        {
                            //tile.color = new Color(255, 0, 0);
                            CalculateDepth(playerRect, tileRect);
                        }
                        else
                        {
                            // If we're not colliding with anything at all, I guess we're in the air.
                            _player.OnGround = false;
                        }
                    }
                }
            }
        }

        private void CalculateDepth(Rect a, Rect b)
        {
            var distX = a.x - b.x;
            var distY = a.y - b.y;
            var minDistX = (a.width / 2) + (b.width / 2);
            var minDistY = (a.height / 2) + (b.height / 2);
            var depthX = distX > 0 ? minDistX - distX : -minDistX - distX; // Calculate intersection depth.
            var depthY = distY > 0 ? minDistY - distY : -minDistY - distY;

            if (Mathf.Abs(depthX) > Mathf.Abs(depthY)) // Resolve along axis with smallest intersection depth.
            {
                if (depthY > 0) // We're hitting the top of a tile.
                {
                    _player.OnGround = true;
                    _player.Jumping = false;
                }
                else // Otherwise we hit our head and need to come back down.
                {
                    _player.YSpeed = 0;
                }

                _player.y += depthY;
            }
            else
            {
                _player.x += depthX;
            }
        }