Not sure I follow. What does the fly have to do with bugs getting in or not? The inner tent's job is to keep the bugs out, the fly is to keep rain out. You can leave the fly off entirely and remain bug free, having a gap at the bottom of the fly in no way that I can see causes bugs to get in.
And I would agree with it. A couple of times, I've used a tent with even a small hole in it. This has led to the sleepless nights of bug hell.
The bugs will find a way in if there are any breaks in the seal. I deal with the hot, muggy problem with a tent with mest ceiling.
I have camped a lot of nights in some of the most bug infested country with the fly left off entirely with no bug problems.