Trial and error, you don't need to cut the rubber at an angle, but make sure you don't have too much jutting out either side of the channel.
Haven't tried out GG3 or 4 yet, at the moment I am using the unger liquid and have been very impressed with it.
I am a WFP convert of some 4 months now, so only use traditional methods when I can't use WFP, but the water I use in my bucket has first been purified as for WFP, so it is as soft as it is possible to be.
There are times when I use very little liquid indeed (unger liquid) and you can almost use the squeegee without any additives at all in the water and it will still glide nicely over the glass
Another bonus of water fed poles methinks
I only heard of dog earing on the forums, glad I did to, stick with it and adapt your technique.
With very small panes of glass I have found that trying to squeegee them in the same way as a large pane is pretty ineffective, either use a spayer with your GG4 in and mist and buff, or use a damp scrim to clean, and a dry scrim to buff.
I have used a small squeegee, but have found the 'amateur' method of one wipe across the glass and wipe the rubber and repeat. But not to much water on whatever you are using to wet the glass with, and edge the panes on the top and side edges quickly with a damp scrim first, that also helps reduce detailing and mopping up on small panes.
Another disadvantage of squeegee-ing small panes is that on the turns, after a day or too, you will see the kicks and lines of your squeegee-ing.
Ian