Compost question

I have 2 dalek type compost bins that I have been filling over the last couple of months. Whenever I top them up the level always drops down after a few days which is what I would expect.

I recently tried to turn over the contents with my fork to try and introduce some air, and even though everything seems to be decomposing it does seem a little damp and wet in the middle - a bit like wet grass cuttings.

I have been composting potato tops, kitchen veg peelings, cabbage leaves, beetroot/carrot tops and grass cuttings. I also throw in the odd shredded paper and cardboard.

I am unsure if I have the mix right between green and brown waste?? Is there any way to tell??

Regular turning speeds things up quite nicely. I run the mower over all the large stuff to get it going quicker, like; potato tops, cabbage leaves, broad bean plants, hedge trimings...