emulsion - why does it make a differnce if you have have more/less water/oil
The two combinations (10/1 and 1/10) of oil and water will give different emulsions: the first will be water-in-oil and the second will be oil-in-water. The difference lies in the continuous phase; the minor phase will be tiny droplets, with a size depending on how much energy you put into shearing it. Neither emulsion will be particularly stable; that's why we need emulsifiers: to stabilize the emulsion, and also to make it easier in the first place.

The yolk of an egg is primarily fatty (that's why it tastes so good). It's so fatty that it does not absorb the egg white, which is 90% water and about 10% protein. The yolk does contain some hydrophilic groups - but not enough to emulsify the albumen. But the yolk can emulsify/stabilize a small amount of water, and the yolk will disperse easily in (some) oils. So the yolk, spread out in oil, can stabilize a smaller amount of water. But you can't get the yolk well dispersed in water: it agglomerates quickly. And extra oil just makes the destabilization quicker and more obvious.