yes, full frame is the best of course and there can be given a very strong arguments for that. i do love very much the 2/3 ratio. (i have past the love to 1/1 and even the 1/2 panoramic). but it is true that it is not always the best way just to put things in thios format. what i do is that im cropping in simetrical way to avoid the problems of pespective and point of view when u crop. when i make image especially on the 23view camera i take it into my concidirations. (for example i can ignore on the gg of the 1cm from each side to make it like 67 format.).
on the small camera it is much more problematic ecpecially on the rangefinder. but i suggest that instead of getting to be used to cropp, it is better to analyze why u want to cropp in order to avoid this cases. the main reasons can be or too short lense or too long distance, so each time it is better to try to match what u realy want.
in the forum of "ethics and philosophy" i wrote in one of the discussions i think "zen..." about the visualization and lenses. with this approach that i work i usually avoid the problems of cropping etc.