You are right, that isn't working for you. A taller ladder will help a lot.
I'd suggest starting with the folks at AutoHome and see if you can exchange your ladder for a taller one. They try to include a ladder that works for your intended rig. It is common to keep the tent when you change vehicles so you may need a ladder that is taller or shorter. I would think they would have a spare ladder they can exchange with you at a reasonable price. Yours looks like a standard height, for something like a Subaru, you need their tall ladder.
They really don't do a very good job explaining how the ladders work and why they are designed as they are. AutoHome tents were originally designed for expedition use, and in areas where you don't see much pavement. The first ladder I saw was a similar design to the new ones but made of steel. It was two parts and didn't lock. The idea is that the two half were designed to slide. You would set up the ladder, hook the ladder to the tent opening and then step hard on the bottom of the ladder. The bottom of the ladder would sink in as much as six inches into the soil or sand, locking it in place. The bottom was in place so then when you got to the top section it was suspended from the tent and as you would put your weight on it you would feel the ladder flex a little as your weight was now suspended by the vehicle. This was normal.
These original ladders were pitiful on pavement, they couldn't get a footing and would slide. Locks or binders were added for pavement on the newer ladders. The old ones were great, you could separate the two halves and use them as sand ladders in a pinch. They were steel so you would just bend them back after.
So, use the locks on pavement. In the dirt or sand, anchor the bottom of the ladder and you don't need to use locks. The new telescoping ladders that I've seen are really heavy, complicated, and don't like dirt in their locking mechanisms. I use AutoHome ladders even though I don't have one of their tents anymore.
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