I think your biggest problem with your approach is that you aren't at all designing a hill, but more of a mound or dome on the ground.
In both cases you have created a rather rapid upward projection bringing the soil level up but leaving it as only a small area of raised land that then recedes back to base level.
The real problem with this is that there is already a best case solution for what you are doing. And that is to revert to the tried and true message of a jutting raise in elevation that is a cliff or firm land mass.
True hills or gradually raising elevations are much more difficult to speak directly. The simple truth is you should probably use a set of tiles for an elevation area and avoid making very small hills that raise quickly and then stop. Show the climb or descent over an area rather than trying to pinpoint it.
I can think of very few cases of this being done on a top down perspective. However I can think of simple small version that you could extrapolate into a much larger version and then use some clever tricks to help people get the message.
In Secret of Evermore there were these little sand dune swirls that give you a good solid idea of raised land. The highlight on one side. The shadow on the other. If you look closely you even get an implication of how it would look on the front/back (north south) angles.
http://vignette2.wikia.nocookie.net/secretofevermore/images/0/0e/Desert_of_Doom.png/revision/latest?cb=20160116031819Beyond this look at any ramps or walkways (not stairs) in top down games that take a player up to a new level that is surrounded by cliffs. Plenty of examples of that. You would of course need to figure out a way to round it and corner it off so that it read well and you wouldn't need a cliff edge to separate areas of greater elevation.
Perhaps go with a more subtle approach like this. Spread it out over an area to give a gradual sense of climbing. Use some other message signals to the player such as a slowed walking speed, or a unique animation for labored movement as they climb up.
Likewise accelerate movement going down perhaps.
Other methods are to not show the elevation at all until you have reached a new area with cliffs or walls separating lower areas that show the player that they have climbed as they moved along. But again this is for a gradual raising land level, not a quick rapid rise like you have been creating.