Highschool Romance/Headscratchers

• Why is Shoji, a boy, shown with abnormally feminine hips, if the drawing are to be trusted?
• How did Hoshi know that Shoji was a boy? As far as I know, she didn't explain anything in her revelation speech, apart from vague words and concepts: "Evidence", the week break, interest, comfort in girl clothes...
  • Then again, figuring that out would have been the easiest thing ever (falsetto voice, no chest, abnormal hip structure).