I take it that you are one that is used to a 3.5 or 5 gallon flush toilet and now are forced to see the 1.6 flush. Most 1.6 toilets do flush well now if purchased in the last year or so. 95% of the bugs are worked out in many cases. However, there are ways and needs to get every drop out of a 1.6 closet(Toilet). First of all, you must understand that the bowls are also designed to flush on 1.6 as well.
One thing that can be done is be sure that the refill tube that goes from the fill valve to the overflow is attached with a clip just over the tube and not down in it. Raise the water level by slightly bending the float ball and rod up. Raise the level to the top ov the overflow. The flapper is also designed to close faster also, not allowing all of the water to flow out. Purchase a product that Fluidmaster makes called an adustable flapper which has a dial on it. It adjusts to different tank settings. If you start at the highest, in many cases the toilet will even double flush the bowl. Some of the earlier attemps at the 1.6 used the bucket around the flush valve or just made the flush valve shorter or the seat higher. Taking the tank off and installing a taller fill valve and flush valve will allow for more volume. Again, you may create the double flush and I have found that many people do like that flush. The Fluidmaster model 400AK will come with everything needed in 1 box. This has a much taller flush valve and an adjustable anti-siphon fill valve. "May the Flush be with you"