I thought the figure four trigger in my picture was pretty much a standard figure four trigger Chrisaloia...although I guess the diagonal stick sits a bit steeper than some.
By having less diagonal stick between the vertical prop and the weight, and a steeper diagonal stick along with the accompanying shorter distance between the vertical stick and the bottom of the diagonal stick, the leverage in the system seems to favour holding a heavier weight...yet requiring only a relatively light force to fire the trap. Because of the leverage set-up, there is less force being transmitted through the 'critical' matching surfaces...the bait stick notch where it grips the vertical stick....so less force will set it off. But this can also make this arrangement a pig to set...it is just so fiddly. Thus it may be better to have less angle on the diagonal, and more overhang between the vertical stick and the weight to exert more force through the trigger...this will create more friction at the critical surfaces and the trap should be easier to set.
That last paragraph might take some mental gymnastics to grasp. Sorry about that. Experience is a much better teacher.
The big challenge in setting up a rock as shown in the 'rat' picture, is having the rock wanting to slide backwards, or twist. When it does either of these things it makes the trigger almost impossible to set.
So if the deadfall weight (eg rock) wants to move I try to jam it against something, or jam something against it, to hold it steady. In the field I might sit a heavy rock against it where it touches the ground. In the picture this rock is jammed against the polystyrene box.
Here are some further figure-four pictures that might clarify the way I do things. The first diagram shows how the trigger holds the weight (rock) in position. If the weight can sway around, or if it has a tendency to slide, then the trigger gets moved sideways and won't hold for long.
At one stage I was tying my diagonal stick to my bait stick. I thought at at the time it may have made the whole thing a bit less 'fiddly' to set. Probably a bigger advantage was that it made the sticks a bit easier to find once the trap had fired.