We have a 2020 BS 3226. Our front curbside slideout, under the awning, had no topper. We had our local selling Newmar dealer install one. With our rig, the above slideout is the exact width as the bedroom slideout on the same side. The awning rail the bedroom topper slides into goes all way to the front---like at one time they installed a topper. It is just below the "real" awning. The dealer got the same Dometic model used for the bedroom slide--BUT Dometic could, or perhaps would, not supply him with a special mount for the flexible metal part which covers the topper when retracted. So I asked the dealer to just remove the weather protector and mount the cloth portion directly into the "topper" awning rail.
With our rig, when you start to extend the awning---it actually goes up a bit, and once out 4-5ft, it drops down. The topper is installed low enough so it never touches the awning above it. When I asked this question back in early 2020, most folks said the always extend the awning. We do not extend the awning often, and when we do we ALWAYS bring it all the way in before bed. We learned the hard way--thunderstorms with wind will rip the awning
We have no problem with ours. but we ALWAYS extend the slide BEFORE extending the awning---when we use it.