There is always a gap when you first cook with your smoker. Even new, this gap isn't big enough to create a "heat loss" problem. Not like the $199 offset smoker you but at the local store that leaks more smoke than a Smoking Room at a restaurant.
Probably need a whole lot more details to determine the issue, if there is one and exactly which one.
Not you specifically, but a lot of new users worry about the details on the cook, instead of just using it as advertised. Sure, there are a lot of details, but they come with practice
IF, and you do have to check, IF it's smoking at the right temp, then there isn't a heat loss problem.
Heck I cook on my FE 100 sometimes with the door open. The smoke will compensate if it detects "cold" temps and just turn on the thermostat to get more heat.