RX3 Bar Risers
No bike is ever perfectly setup for every rider. With heights from under 5ft to over 6ft, there's no way it could be. You can change the seat and alter the ride height to partly compensate for height, but for an even better fit the only thing that's really left is the position of the handlebars. They can be rotated somewhat and that will shift riding position, but to really change their height and distance from the rider you need at add bar risers.
There are lots of commercial bar risers available such as the ones from Tusk shown on the left. They come in 15mm and 30mm sizes. Just make sure you get the ones for 1 1/8" bars, not 7/8" bars and ones that will actually fit the hole spacings and bolt sizes of the RX3. Of course the RX3 isn't one of the bikes in their compatibility chart, but I think that the ones made for the BMW 800GS fit the RX3. However you might want to check that with the vendor. I haven't purchased them myself, so I can't personally guarantee they will be the right ones.
If you're mechanically inclined and have the tools to do it, there's an easy way to make bar risers for the RX3 yourself that allows you almost any degree of rise. The cradle that holds the bars on the RX3 isn't an integral part of the top of the triple tree. It's actually just bolted on there with two bolts. It's easily removed and you can then fit a spacer of any height to raise the bars. There are some limitations though. The various cables, particularly the front brake hose, limit how much the bars can be raised. You can probably get 1" OK, but much more than that and you'll have to modify (lengthen) at least the front brake hose. I don't know how far the wiring looms will allow you to raise the bars. If you added lots of rise I'd start to worry about the strength of the whole assembly, but for an inch or so (which is typically what most people will use) I don't think that's a concern.
The cradle for the bars is attached top the top of the triple tree via 10x1.25x25mm allen head cap screws. If you raise the bars with a spacer you'll need longer bolts. For a 20mm raise you'd need something like 10x1.25x45mm or 10x1.25x50mm bolts. Check the thread length on longer bolts since they typically will not be threaded all the way along the shaft and you need to be able to screw them in at least 20mm, so you need 20mm or more of threaded section coming out below the spacers. Then all you need is either a spacer plate or two individual spacers to lift the bar cradle. I made mine out of 3/4" aluminum round bar since it's what I had on hand. I might have used 1" bar if I had had any. The ones I have now are about 17mm and they fit just fine. You need a hole slightly over 10mm for the bolts (13/32" works fine). I suppose you could use a stack of washers, but I'd be a little worried about the strength and stability of a stack unless the washers were perfectly flat.
A flat plate with two holes could also be used. For example for a 3/4" spacer you could use 3/4" square aluminum bar. You need a piece 4.5-5" long. You will need to remove some material around the nut steering head nut if it contacts, but that's easily done with a file.
One useful feature of using flat spacers is that you can easily (and cheaply) stack them. If you start out at 3/4" and want to go to 1", you can just add 1/4" spacers.