looks like you had your speed too high and you were moving to slowly, you got it to pool, but you didn;t move quick enough. did you drag the weld or push it?
can;t watch the vid as i don't have strong enough signal, but that looks a smart place to put it.
Husky did this to his exhaust but he put it off the Y pipe, it was so loud under the car it made ears bleed, and not in a nice way. the sound was great either.
exhausts are a bit like instruments put a hole in the wrong place you get a bum note. same as you can tune them with resonance chambers. but i like your idea of bypassing the rear muffler. means your not de tuning the exhaust just cutting a muffler out. and it keeps the flow straight.