In my experience, these bikes aren't super sensitive to jetting unless you start getting into ported (highly tuned) engines.
Every one of my KDX200's or 220's have had an FMF woods or fatty (or pro-circuit), with close-to-stock jetting. Im at 950 ft above sea level so we should be close.
All of that said, Im not an out and out "Expert" on trying to get the last Nth-degree of power out of them... I've had a bunch (insert shameless plug for the 2 I have in the for sale section...lol) and all of them run just fine. Some had aftermarket reeds, and once again, all have had chambers (FMF or Pro Circuit pipes).
One thing I am an expert on (Ive got a few melted pistons to prove it) is that on a two stroke engine that gets its neck wrung, The highest octane fuel you can feed it, the better..up to a certain point.
Detonation (pre-ignition) is the enemy, and if you are starting to find yourself jetting "lean" to get power, you are going to be putting another piston (and possibly worse) sooner than later. 87 Octane is just asking for trouble....
At the very least run 91 or 92 Octane pump gas. Im not saying its going to "fix" any of the lack of power issues, but it may save your engine.
There are a few bright guys over at KDXrider.net. Someone should know exactly what you need to get every ounce of hp out of it, without the flat spots..