Hard to give this kind of advice without back and forth, so I may need you to email me some pix...but here goes!
For flate photos, better to set up so that you can get more distance between camera and food.
So a lower table or a higher tripod that allows you to mount the pole sidways so the camera can be placed directly above a subject.
You are having the problem I had with my alogrithm shoot I mention below...
35mm lens is going to give distortion on the edges, plus on a crop sensor it's not going give a much wider angle.
D5600/7200 are both the same megapixels, so there won't be an increase in quality, but are newer cameras so the chips are probably better quality.
D7200 would be the better choice if ye the wealth...
Other factors are potential camera shake, either too slow a shutter speed, not using a tripod, or not enough depth of field.
Hope that helps, if not email me some pix!

So much... 1. Doing this every day is hard. It's actually a lot of work. Well, at least trying to come up with something worth reading and not dumb two lines quotes of blathering nothingnesss... 2. I really need a wireless remote for my camera. 3. Some idiot put an illegal deer stand in a tree on my property that I'm not sure how to deal with. 4. People apparantly want to see more dancing... 5. The survey was super enlightening, will be sharing the results soon, but here are some teasers I found the lack of Star Wars fans among my survey respondents...disturbing... I was surprised for the lack of love for Capatin Sisko and Captain Ron... "Your very name is a lie. It says no 'L' but there it is, mocking me."

Inside, there is one set. Carpeted. Off white, with flecks of red and blue. Wait, are you casing my house to rob us? If that is the case, it leads to a pit full of alligators...

If I did, I wouldn't be able to reply. I'd be dead.

I think it's really not a question of how much wood could a woodchuck chuck chuck if a woodchuck could chuck wood...but more of a WOULD a woodchuck actually chuck would if a woodchuck could chuck wood...

Do I look that flexible? I had to combine separate images. One with my chest area raised, another with my legs flying up in the air...

They all have some layer of difficulty. Mostly from trying to shoot them without a wireless remote and not having an assistant.
One of the hardest things is framing the image properly, and getting proper focus where I am going to end up.
One of the most difficult was the algorithm shoot. (Not the dancing one, the one with the charts, etc)
First I had to create all the charts and calculations, etc. I had the camera on a tripod with the bar sideways hanging over the table. I had to arrange everything perfectly, leaving space for myself. Then I had to hit the self-timer, climb under the tripod legs without hitting them, and get into position.
The table is about 8 inches off the floor, so I had to lay down on the floor, but then arch my upper body onto the table so it would look like I was asleep on a table. Otherwise it wouldn't right. That was really uncomfortable.
And I had to repeat this over and over again, because by this point my kids were sick of being my assistant no matter how much I offered to pay them.
My pec muscles hurt for a few days afterward, probably from not being used to have to actually do work.
My ab muscles were the same after the birdbox/cinammon/planking challenge. That was also hard because I wasn't able to learn both my upper body and my legs at the same time, so I had to cheat and shoot them separately and photoshop them together.
And finally, the one with our poodle Pepper also happened as I described. She did not want to co-operate at all...