Gee ferdy, thanks for your constructive input. ANYONE could expect such grip with even a negative angle on, because maintaining grip upside down makes total sense, especially something that weighs more than the standard tackiness threshold is meant to. Next time don't waste your time and your electricity posting such useless comments.
UsakoKirei, yes you should use water. Water won't dry the rubber out and will help lift off the dust and oils, use a sponge and wipe. TT cleaners work, but most other stuff contains a bit of alcohol or destructive chemicals that dry out the rubber and make it brittle.