@celia come again? I don't understand the question.
Bridgy parses the microformats and decides based on your options and the target what is used.
You can use "full content" out of the box but if your target is e.g. TW and you provide a summary Bridgy will probably pick the summary as it is described in the About.
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.