You should look at this video posted by brianhomer where he shows his final project.
The project consist of using InMoov hand controlled through an Arduino with a power glove made by himself.
The demonstration with the can definitly shows that finger tips need to have silicone patchs in order to grab objects correctly.
I have stumbled on a material that could be perfect for this use, I haven’t tried it but it seems promising and easy to use.
Google: sugru rubber
This material could be applied by hand directly on tips or even casted in a printed mold…
Anyway it seems a much easier solution then the one I used on my first hand.
Another thing about brianhomer project is the fact he used only one cable per finger which makes the return of fingers « uncertain », but he plans on building a second hand so I hope to see totally fonctionnal.
I contacted him to see if he would be kind enough to give me the Arduino sketch he came up for his power hand, it could save us time.