Many thanks for your helpful info and suggestion.
I'm sceptic on size M Altena as Dahon specifies that it is for 157 - 172 cm. rider height while size L is for 170 -195 cm.'s. However if size L's cannot be got hold of, I might weigh and compromise on sizing keeping your suggestion in view.
Btw for my sizing comparison info, could you give the top tube length (c-c) and wheel base of your Smooth Hound (presumed size M) ?