Exhaust location

[eighteenninetytwo]

I'm going to be running a soft topper for the 1975 Blazer and I'm wondering about exhaust fumes with the kids in the truck. Recently I've been carrying long chunks of timber and driving with the rear window down. I've notice that exhaust fumes tend to come into the truck when this happens, no matter whether the front windows are up or down.

The exhaust system was fitted by a generic muffler shop, NOT a Blazer specialist, so are they in the wrong position?? (see picture)
.....ORRR is this just something that happens with the rear window down and a hard top???
.....ORRR is it just something I have to get used to with a soft topper( I'll probably run safari style with no sides).