I just received a beautiful IWB "Double Clip" from Side Guard Holsters (I'll be doing a review on it later this week when I have time to get some pictures). It's my first IWB rig and I, too, am going through a little trial and error getting used to it.
As a test (and to break it in a bit), I wore it while mowing my (1.3 acre) lawn (with push mower) and doing other various yardwork today - a pretty through test of comfort for a holster in my book.
I find around 3:30-4:00 to be the most comfortable, but not the most concealable position. A t-shirt alone does not really make it "disappear" at this position, but it was comfortable to wear for several hours of physical labor.
I also found it is more comfortable if I let my pants ride a little bit lower than I usually do. Try adjusting the height of your belt, and the tightness of your belt also. A good, thick leather belt makes a big difference, too.
Basically, explore all the variables you can. Holster, position, belt, belt tightness, height of pants, etc...
I think it comes down to trial and error. Finding a holster design is one step, and finding the right spot to wear it is the next. The last step is to practice like mad with whatever you end up with I think you have a good selection, just find a spot that works. As I said above, try adjusting other things like how high you wear your pants and how tight you keep your belt.