Toot,
Yes and no to your question about chest and sighting.
I never have made a petronel, so must go off others comments, but a gun could be held/braced against the upper chest could still align the sights (tube rear sight as you found in your case!) with the eye.
I'd need to see your petronel, as some have a very long and deep curve to them, so using in this manner would be no problem. (If that Is how they were held)
Pity I'd have to mess with uploading a photo to my image hosting site, Then here, so it won't happen tonight, but maybe I can get one up showing what I mean fairly soon.
You have been using a matchlock a long time Toot, so you can't 'blame ' me for it! LOL!
Re this thread, Matchlock shooters?;
Built my first decades ago. Was inspired by a wild mate from Sheffield originally, who built archaic guns and chased goats up and down the Nelson Range of Kiwiland with them. He said for reliability, the palm must ever go to the matchlock, so I Had to make one!
It was a fish-tailed stock type, with inlays in the English/German/Dutch fashion.
Got a mule deer buck with it that first season, at about 85 yards. Smooth 20 bore barrel, Length of hunt was about 18 inches of matchcord.
My a bit wild pal is a certain Maurice Taylor. He came over this year to out annual shoot we host on the farm here in Alberta in June.