Of course, I assume that the same amount of coffee is used for both cups.
In that case:
Caffeine dissolves very readily in water. The caffeine content in your cup is mainly and almost solely determined by the amount of coffee you use. The impact of any other factors such as amount of water, water temperature, and pressure are negligible.
To get a rough ...
Generally, the "extraction" happens when the coffee is in contact with the water. So from the initial point of contact in this case the bloom phase pour till all the water (with dissolved solids) is removed from contact with the grounds.
Technically speaking, The initial small quantity pour and stirring in your recipe is the bloom phase and the ...
The easiest way to make the texture of your coffee thicker would be to increase your brew ratio - use more coffee and less water while brewing.
Also don't be scared to use higher temperature water, even if the inventor recommends ~80°C water, this is also going to increase extraction, leading to a higher percentage of dissolved coffee in your cup.
You might ...