I want to see a picture of that trap after you install it reversed.
The problem, as I understand it, is the wall drain is too high to maintain a level or downward slope from the trap. It is low enough for a standard sink but the installation of a disposal lowers the height of the trap. This plumbing was probably done before disposals were as common as they are now.
Solutions are a shallow sink or re-plumb the drain.
Note that the input neck of a trap is longer or higher than the output. This limits how high the trap can be raised. The first picture shows the normal installation. The second shows the trap installed in reverse or backwards. The outlet is now considerably higher (relative to the input) and proper slope of the arm to the wall drain can be achieved. I have shown the disposal elbow inserted in the trap the same amount in both pictures. It is inserted in the reversed trap its maximum amount, which is only about 1", but is sufficient to seal. The disposal elbow may have to have an extension to get back down to the level of the wall hub.
When I decided to photograph rather than just describe this, I went to the shed to get a trap. I had traps but did not have the arms. I decided to go to Home Depot and purchase what I needed. After all I could always return them. Well that HD has to be the worst in the country. They never have what you need and if they do, you can't find it because its not in the right place. When you get to the register the price will be different. The only thing they had in 1 ½” were J bends and one arm. In the third picture the J bend on the left is what I am accustomed to seeing. It has a “normal” length input neck. It was the only one they had like that. All the rest were like the one on the right, it has a shorter neck. Note the difference in the height of the output. It is approximately 1” higher relative to the top of the input. I don't think that this is a different version of a J bend, it was just probably made in China where they shorted the material. It may be just what gczza needs, not a trap with a deeper throat but one with a shorter input neck. Or just turn the trap around.