https://qiita.com/ohbashunsuke/items/fbe423ac10dd4dbf4ce2
こちらの記事で便利な機能が紹介されていたので
SceneViewでどれくらい拡大されているか見るGizmoを書いてみました

表示と一致しているか確認

RaycastPaddingDrawer.cs


using UnityEngine;
using UnityEngine.UI;

#if UNITY_EDITOR
using UnityEditor;
public static class RaycastPaddingDrawer
{
	[DrawGizmo(GizmoType.Selected, typeof(Image))]
	private static void DrawPadding(Image image, GizmoType gizmoType)
	{
		var pivot = image.rectTransform.pivot;
		image.rectTransform.SetPivotWithKeepingPosition(new Vector2(0.5f, 0.5f));
		image.rectTransform.ForceUpdateRectTransforms();
		var center = (Vector2)image.rectTransform.position;

		image.rectTransform.SetPivotWithKeepingPosition(new Vector2(0f, 0f));
		image.rectTransform.ForceUpdateRectTransforms();
		var leftBottom = (Vector2)image.rectTransform.position;

		image.rectTransform.SetPivotWithKeepingPosition(new Vector2(1f, 1f));
		image.rectTransform.ForceUpdateRectTransforms();
		var rightTop = (Vector2)image.rectTransform.position;

		//CanvasのRenderModeに対応
		var width = Mathf.Abs(leftBottom.x - rightTop.x);
		var ratio = image.rectTransform.rect.width / width;
		image.rectTransform.SetPivotWithKeepingPosition(pivot);
		image.rectTransform.ForceUpdateRectTransforms();

		//マイナスにすると広がるので値を反転させる
		var padding = -image.raycastPadding;

		var left = center.x - image.rectTransform.rect.width / ratio / 2f - padding.x / ratio;
		var right = center.x + image.rectTransform.rect.width / ratio / 2f + padding.z / ratio;
		var top = center.y + image.rectTransform.rect.height / ratio / 2f + padding.w / ratio;
		var bottom = center.y - image.rectTransform.rect.height / ratio / 2f - padding.y / ratio;

		Gizmos.color = Color.green;

		Gizmos.DrawLine(new Vector3(left, top), new Vector3(right, top));
		Gizmos.DrawLine(new Vector3(right, top), new Vector3(right, bottom));
		Gizmos.DrawLine(new Vector3(right, bottom), new Vector3(left, bottom));
		Gizmos.DrawLine(new Vector3(left, bottom), new Vector3(left, top));
	}

	// MIT License 
	// auther : Kohki Nakaji@nkjzm
	// Link   : https://qiita.com/nkjzm/items/297fb6921d5caca3eca9
	public static void SetPivotWithKeepingPosition(this RectTransform rectTransform, Vector2 targetPivot)
	{
		var diffPivot = targetPivot - rectTransform.pivot;
		rectTransform.pivot = targetPivot;
		var diffPos = new Vector2(rectTransform.sizeDelta.x * diffPivot.x, rectTransform.sizeDelta.y * diffPivot.y);
		rectTransform.anchoredPosition += diffPos;
	}
}
#endif