From what I know/experienced, the Zois use the nearest counter to the fridge to prepare the food. Which in your case is the one with the sink.
What you could try is to place the sink on the next counter.
I have exactly the same problem. I tried to put another sink, but it does not help. It is strange, why not set the sink as an object?
Have you tried placing the sink on another counter that’s not the nearest to the fridge?
It’s a workaround until it gets fixed, inZOI is still early access.
I have only three bellies in my kitchen. One is impossible to approach, the other is next to the stove. No one puts the sink next to the stove, and I am for realism. Besides, this problem can be easily fixed right now. We let the developers know about it
Maybe it is even a feature for such small kitchens like yours 
I sometimes put a cutting board on my sink too ^^’
Looks like you need to rearrange the kitchen in some way, even if it means moving the fridge or stove. I have done this in all my houses, as it does bother me seeing the food prep teetering on the edge of the sink! Perhaps you could put in a counter island? That worked nicely in one of my smaller kitchens.
This did not used to happen, but there have been some updates to how counter tops work, and (I assume) as a result of making it possible to use counters when they have decorative items on them, they can now be used even when they are occupied by a sink.
I think the system is deliberately intended. And I like the system. Because I prefer cooking by the sink rather than on the counter. It’s easier to clean up any food that splatters.
For me, this only happens when my Zois cook foods that involve cracking eggs. All other foods are cooked on the normal counter spaces.
I wonder if this is intended. Throw the egg shells into the sink lol
That is a good point, I have noticed that foods involving eggs (maybe foods that go in the oven in fact?) tend to be cooked on a different surface. In my case, on the counter island, which is also close to the fridge but in front of it rather than to the side.
How odd…
whoa, and I love this bug)) I have more places in kitchen to put smth beautiful there, while my Zois are cooking on the sink 
(p.s. cuz I have a very small kitchen))
From what I have seen, Zois will now prepare food on counters that have several decorative items on them. Kitchen clutter ftw!