I found with the chesty – ditch the bracket that it come with (longer curved one) and use the normal one, have the camera upside down, in upside down mode, tilted down as far as the bracket will let you. Have it low-ish, where your sternum ends and tight so it wont bounce around.
On the down tube is a good angle, pointing forward so you get the forks in shot doing the trombone. Do that with the helmet mount and a bit of gaffer tape. Also seat tube pointing back looks good if there is some one following you; or forward for a mostly bike angle. Pointed at the rear shock for a few seconds of “look how much travel Im using”. On the bars pointed at you for the grin shot…..
Don’t forget the submerged in beer finale.
Hours of fun! 😀