I evaluated what you are considering and decided to send my tarp back to Joe Valesko to sew on the bug screen. It seemed lighter overall than a separate bug screen.
However, shoulder seasons justify your decision. I tested my ZPack Hexamid Twin with extended beak this past weekend. The tarp did take more room in my pack and now weighed 5 oz more. It was way too cold for bugs in the high mountains of Colorado so having a separate bug screen would have been good this past weekend because I could have left it home. I'll be out again next weekend and I bet there won't be bugs in Colorado mountains yet either.
But from June through September, I'll have a lighter overall option for bugs. That was my reasoning.