when i manual i do keep my pedals level with the top tube, i basically just keep them where it feels natural
something i can add: when i learned manual, what made it possible was seting goal. i would pick a couple cracks on the ground then try manual from one to the other. once i get that pick a bigger gap. this kept me motivated
Probably the best bit of advice ive heard in awhile, setting personal goals and acheiving them feels sooo great!