Here is a drawing of an exponential crank taken from Bob Baron's Humbug article, with a longer pushrod arm, so you can see the exponential better. A pin in the bellcrank drives the pushrod arm via the slot. The depending on the exact location of the pivots, the pushrod hole moves about 20% further than if the arm was fixed on the bellcrank, and the movement increases(pushrod force goes down) as the mechanism moves. This means you have to allow for the forces on the elevator, and they have to be lower than on a standard plane, or you will may run into the "Netzeband" wall going into the wind.
Fred Bachle moved the expo arm pivot to the other side of the bellcrank pivot, allowing somewhat better leverage and a faster expo rate. It necessitated a fairly complicated expo arm to get around the bellcrank pivot.
Any setup where the connections between the lines and the pivot(both at the handle or at the bellcrank) are not parallel and straight lines require you to carefully fine tune the neutral adjustments through out the control system so everything (plane, controls, handle) are at neutral at the same time so you don't introduce control feel problems. You can see if the handle neutral, the bellcrank neutral, and the controls are not all exactly neutral a the same time the control feel will change as the controls are moved. You get the similar problems if the handle overhang and neutral hand axis are not all squared up too. See the thread on how a bad neutral can cause a crash.