Re charging voltage and onset.
I am not sure in understood your question, but I have observed no changes in charging voltage or onset of charging. Nor would I expect a y change, they ignition and charging systems are unconnected.
Re brackets. I have bought brackets that mount where the bolts the R65 doesn't have at the rear of the tank go. This places the ICU upside down above the aircleaner ; fine for a flat pack filter,. It I suspect no so great for clamshell filters. These brackets are available from Munich Motors in Australia. I will photograph them tomorrow.
Other mounting options are cable tied to the main frame under the front of the fuel tank - a contact says they have been running their unit in that position for 10+ years on a bike not originally equipped with electronic ignition.
An option for early R100 and 1981 R65s is to simply drill the heatsink with holes the same a dry apart as the original ICU and use the original mount.
I asked one of the designers and was advised they were not only OK with that, they do it themselves. Simply used a transfer punch to mark centres and had at it in the drillpress.
Re EI units. I noted the less advance than advertised, but ask set timing at 3,&00rpm it took a while for the penny to drop that there was a problem.
The thing does seem to be capable of 26 degrees of advance,. It there seems to be a variation due to heat, voltage, or both and it rarely exceeds 22 degrees.
I now set ignition, at 3.5k to an estimated 2 degrees less than full advance. If the ICU fails to fully advance I still have around 24 degrees of advance, and if it does then I have approx 28 degrees of advance. that will not stress the engine so I simply stopped worrying about it. This is less variation than I measured across a sample of early and late flywheels that led me to conclude that the Romanian guest worker employed at the factory to punch the flywheels had some random days.