Beyond a size increase, it needs to be more 3-D. Here are a few ideas that work for the Jap reels. I picked up a very similar power handel (all metal) for the saltiga and it is comfortable and while it looks a little odd you don't get fatigued. Here are a few ideas.
Like this:
http://www.tsurishopjapan.com/popup_...0af6a4fce2a4fc
or
http://www.tsurishopjapan.com/popup_...a83770bc74d6a0
or
http://www.tsurishopjapan.com/produc...0af6a4fce2a4fc
and the arm should look more like this:
http://www.tsurishopjapan.com/popup_...0af6a4fce2a4fc
http://www.tsurishopjapan.com/popup_...a83770bc74d6a0
http://www.tsurishopjapan.com/popup_...0af6a4fce2a4fc
Actually the one I got for my saltiga is the bottom one on this page. It is not perfect but it is far better than the original and the arm was a tad longer which makes it very easy to reel. The feeling of mechanical advantage when reeling is pretty dramatic. (like a trailer winch)
http://www.japantackle.com/Tuning_pa...a_spinning.htm
For me, my favorite handle shape is the egg shape, it just feels good.