A funnel can be so many different things. I call it hunting the terrain because its not always a funneling effect. Its basically any feature in the terrain that concentrates travel. You also need to have something deer want on both sides of a funnel such as cover on one side and food on the other. One of my basic funnels is a steep hillside along a deep creek the hillside and creek run about 50 yards apart. On one of the creek bends it bends in towards the hillside and creates a funnel where they become 10-15 yards apart.

Another settle funnel I hunt is simply less aggressive slope coming out of a hollow.

Going around ravines, traveling saddles across fields etc

Definitely not just a depression coming from a hilltop. Deer would actually funnel away from something like that in some cases.