Trying to finish basemnet. Previously there were two round branches coming out of furnace/trunk they were running side by side. One branch was 8" and one was 7". Would like to make soffet smaller. Could I instead put it in a tee in 8" and tap a 7" in the end? Just wondering if this is going to mess up air flow. Please see pictures/attachments. The bottom one is where I want to tee into. The top picutre has a sheet stuffed into it. That's where the 7" used to run next to the 8"''. I have it completely removed at the moment.