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.