I don't know if you have got any further with this.
A follower left me a message, saying that she actually saw only a summary in her email notification when another told me that she saw full text. After asking further questions, I realised that not only my blog language and interface language had to match, my followers' interface language also had to be the same as my interface language for the summary view to work. In other words, if a follower's interface language is different from mine, they see full text in their email notification; if it's the same as mine, then they get a summary.
I will be grateful if you can fix this. It's not good if bloggers and their followers have to synchronise their interface language.