Slap this baby against an edge and let it extent the visual effect below the safe area, but not the content view.

SafeVisualEffectView.swift

//
// SafeVisualEffectView.swift
// Created by Rob Amos 2018-08-19.
//

import UIKit

open class SafeVisualEffectView: UIVisualEffectView {

  // MARK: Initialisation

  public init(effect: UIVisualEffect?, extendableEdges: UIRectEdge = .all) {
    super.init(effect: effect)
    self.setup(edges: extendableEdges)
  }

  public required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    self.setup(edges: .all)
  }


  // MARK: - Setup and Layout

  private func setup (edges: UIRectEdge) {
    guard #available(iOS 11.0, *) else { return }

    self.contentView.removeConstraints(self.contentView.constraints)

    let constraints = [
      self.contentView.topAnchor.constraint(equalTo: edges.contains(.top) ? self.safeAreaLayoutGuide.topAnchor : self.topAnchor),
      self.contentView.rightAnchor.constraint(equalTo: edges.contains(.right) ? self.safeAreaLayoutGuide.rightAnchor : self.rightAnchor),
      self.contentView.bottomAnchor.constraint(equalTo: edges.contains(.bottom) ? self.safeAreaLayoutGuide.bottomAnchor : self.bottomAnchor),
      self.contentView.leftAnchor.constraint(equalTo: edges.contains(.left) ? self.safeAreaLayoutGuide.leftAnchor : self.leftAnchor),
      self.widthAnchor.constraint(greaterThanOrEqualTo: self.contentView.widthAnchor, multiplier: 1),
      self.heightAnchor.constraint(greaterThanOrEqualTo: self.contentView.heightAnchor, multiplier: 1),
    ]

    NSLayoutConstraint.activate(constraints)
  }
}