I have many hours on Dash 100/300/400. All are easy aircraft to fly, but a nice landing has to be gentle and pointing straight down the runway. If you are pointing anywhere else it will give a jolt (unless the runway is wet). Once you are on the runway, it sits there because of the wide stance - that is nice when the weather is bad.
If the tires and oleos are all at max pressure, every landing will feel firm. Don't take it personally.
The reduced pitch stability and flat attitude at flap 35 can make those landings more difficult, but with a little practice its not that hard.
Tailstrike attitude for the 400 is 7.5 degrees. Stop flaring at 5 degrees and use a bit of power to cushion anything after that.
I find the 400 most difficult to land nicely because you need power on, and it is too easy to float .... then you start to drift or need to drop it as you are running out of runway. Also the 400 has momentum when you kick it straight - it is easy to over correct.