Are you using an adapter for the lever/pod interface?Is it an actual Shimano Pod?
I have a Shimano SL-7800 DT shifter lever on my Shimano bar end pod.
Ideas:
1. Maybe your limit screw needs to be let out a bit to let the lever travel far enough so it will click?
The shifting does get a bit tricky when you reach either of the ends. The shifter seems to run out of room and doesn't quite click as smoothly. However, with some fine tuning of the tension, it will shift to all gears with no problem (at least on the Betty).
My SIS indexing works great across the whole cassette. So I think yours could too. I feel no resistance when moving the levers. Every gear change clicks nicely, even to the extremes of the cassette.