Rice – Bringing water to boil with rice or alone and then add rice

There shouldn't need to be any variation in the water at all, since the things that you are adding are already hydrated and are not taking in any water. Indeed, it would be possible that some vegetables might even give off water.

I would be more inclined to look to whether you are measuring accurately every time you use the rice cooker (just asking) and then, if so, whether your rice cooker is consistent. I had an inexpensive rice cooker that I liked for the convenience, but it was inconsistent on turning off, so the results were a little too varied, OK for me, but not when I was serving other people.

The only other thing to consider is that many rice cookers work on a temperature principle...when the temperature starts to rise (meaning the water has been absorbed) the cooker shuts off. If the ingredients you are adding are raising the temperature of boiling (as in a lot of salt, say) then it is possible that you cooker is shutting off before the rice is cooked, and then the water is absorbed or evaporates, but the rice cooks no further.

I would pay very close attention to your measuring (rice and water) for the next couple of batches and see if that fixes the problem.

The basic differences between white and brown rice is explained below (as written here):

An important first question to ask about all rice-and for that matter, most foods-is how much it has been processed. In the case of rice, processing usually involves milling and polishing. The outermost layer of rice, called the hull, is removed to make brown rice. Brown rice is rice with the whole kernel intact and the kernel is still surrounded by all layers of bran.

To produce white rice, the bran layers of the rice have to be milled off. Most of the rice germ is also removed during this abrasive grinding process. At this point in the process the rice is called milled, unpolished white rice. Finally, a wire brush machine is used to remove the aleurone layer that remains on the rice. This step is called polishing. As polishing is not an all-or-nothing process, semi-polished rice may still contain parts of its aleurone layer.

Additional information about brown rice (here):

[Brown rice] has a mild nutty flavor, and is chewier and more nutritious than white rice, but goes rancid more quickly because the germ—which is removed to make white rice—contains fats that can spoil. Any rice, including long-grain, short-grain, or sticky rice, may be eaten as brown rice.

So, because they are processed differently and have different parts of the grain intact or removed, your method of cooking is going to vary.

I have used this method of cooking brown basmati rice with pretty good success. It includes washing the rice a number of times prior to cooking and adding salt. This method advises adding oil after the cooking process, but I typically add it into my rice while it cooks, or even sauteeing the grains in oil then adding water to the pot to cook.

It is also suggested that leaving your brown rice to soak for 15-20 minutes (and sometimes even longer) can be beneficial as well.

All of that aside: if you're looking to stick with a flavor and texture similar to that of white rice then brown rice may not be your thing. I know that as a jasmine rice eater I do not particularly care for the texture of brown (even brown jasmine). As mentioned above it does have a "nutty" flavor and is "chewier" regardless of how well/properly it is prepared. It changes the flavor and feel of every dish I serve it with. Just a heads up.