I don't know if I'm understanding your question correctly, but generally even smaller cards (as in less tall) tend to compartmentalize the case in such a way that hot air in the GPU "compartment" gets trapped and recirculated to some degree. This is a known issue for all open air coolers and will be for the strix too. A few ways to mitigate this:
1. Bottom fans: Increases air pressure in bottom compartment and helps push cold air into the GPU. Problem: Noise, and it would ruin the entire point of fan less mode which is the main selling point of the strix.
2. Ducting: Bottom ducts that force the GPU fans to get air from under the case on the outside. Problem: Hard to make it look nice.
3. The PCI bracket plate: The plate thet screws in over the PCI brackets on the back of the case can be removed to offer significantly improved air exhaust capabilities. Some people have reported a 5C temp improvement by doing this.
This issue doesn't need to be a deal breaker, but I suspect it might be hard to keep the temps down there low enough over time to really benefit from the fan less mode of the card. That is just my guess though. I would (and plan to) go with a short itx-style 970 instead. It should offer way better airflow.
I used the 970 Mini in my build and temps aren't excessive under load. Internal case temp hits ~50-55C under heavy gaming load. This is with no ducting or fans underneath, so it seems like air is able to move around well enough. I'll try removing the PCI bracket plate as mentioned to see if it helps.
One downside to the 970 Mini is that the fan doesn't have a silent mode - it will always be on. It's very gentle at idle though, so you probably won't hear it over the other system fans.