How to paint rough but distinguishable people with oil paints? I've been teaching myself wet on wet expressionist style oil painting lately and my landscapes, cities look awesome. But...

But when I go to add some small detail in amongst the fray, particularly people and other non geometric objects, they end up blobs of mixed colour. With a knife, you can scrape a shape to clarify  confusing details, but small, complex objects are just hard... especially people.

If the colours didn't just merge with the background, people would be easy, but they don't obey me.

Bob Ross says use thinned paint to paint over the background, but this doesnt seem to work all that well for people :(

Edit:



As per request, here is one of my paintings. A small representation of an ancient city. I finished it dissatisfied that there were no people in amongst a city, and so wanted to add them to give some nice perspective, but never intended for them to take over. However, the first reaction my brother had was 'what is that?' - and I would agree. I wanted them to be dark blue to fit with the theme, but adding a dark blue figure (and her child) just blended straight into the wet background on the left, and thus in a last ditch effort I repainted the character on the left in grey with loads of thinned oil paint and tried to add small blotches of skin tone to the face in order to push the concept of a person. Nevertheless I am pretty displeased.

Because of her blobby she got, it became hard to give her a reasonable pose or make her look.. Good.

On the right a couple are (supposed) to be walking away from the audience, but really they are nondescript blobs. They fit in with the colours, but with no discernible features.



Perhaps I'm too picky.
There are a few things to consider, that I can think of at the moment:


This merging with the background and the blobs are actually the charm of the technique. You either learn to use it to your advantage or find a technique that serves your means better. (You can mix techniques, too, of course.)
Generally speaking, wet-on-wet works better on larger scale canvases because of the smudge-like nature of the technique.
For applying paint in detailed manner get a fine brush, either flat of pointed. The ones I'm referring to are actually not meant to be used for oil (I think) but they work fine with it (as long as they are not the ones with ultra-soft bristles; all brushes for oil need to be fairly stiff). You will still have some mearging with the background, though.
You can add fine details to your painting without the merging by letting the layer you've painted dry a bit and then paint on top (but this is not wet-on-wet).