How to make a very DENSE mocha?

The mouthfeel of a mocha is based on the milk. More precisely, the creaminess that comes from the tiny bubbles in the steamed and frothed milk. You get the “fullest” or “densest” effect when you create a microfoam instead of large bubbles and a stiff foam.

Apart from that, the ratio of milk in a mocha is significantly higher than the 20% you are using right now - and without enough milk, you end up with a watery drink, unless you are using specific thickeners.

In short, add espresso and chocolate/cocoa to frothed milk, not a bit of milk to a large amount of coffee. That said, there’s of course nothing wrong per se with your ratios, especially if you like the flavor, just the dense texture will be impossible to achieve without using a suitable thickener.

Posting comment on original question as an answer to benefit the Google creepy crawly bot.

Mochas are latte-based drinks. They use steamed and frothed milk, not just plain milk. Steamed and frothed milk are both produced by mixing air and heat with milk (typically by injecting steam, by heating and agitating, or by a combination of these) to make it creamier. You can make frothed milk without special tools by agitating milk aggressively while heating it on the stove. Use a hand mixer or immersion blender. If you like the effect, you can buy dedicated frother devices for about $30-40 online.