You are missing my point. The emplacement is only another element amongst others to be at least suspicious about the historicity of the "Battle of Covadonga". I have recalled several other elements, mainly about the symbolic elements around the event. If you think that this is irrelevant, wether we are talking about a matter of historical events or an historical propaganda construction with legitimation intents, I can't say anything else.
All battles of the conquista, from the first raids of 700's to XI century were heavily mythified, magnified or even totally invented by any side in presence (Asturians, Basques, Odonids, Carolingians).
We're forced to "reconstitue" elements with the few sources avaible (chronicles, historians, archeology), but until we can say that a battle never occur (as Clavijo) using this name (being aware of the blur about it) is better that don't caring about what we have to take all this from zero.
All this period was historical propaganda, i can't honestly think of one relation of battle that didn't was totally re-written. And all of them are not to be saw suspiciously.
For the symbolical history of Covadonga before the "Kingdom of Asturias", you're right. But if the battle occured it, it wouldn't the first time that an already charged (symbolically and culturally) would have been the theater of a more recent event.
And,
if the battle occured in this valley, among many semblables places avaible in a relativly fortified aera around Europa's Mountains, why not indeed invest a place already known and having a strategic importance?
I'm not saying that it was the case, but the cultural and symbolical change of this aera from a more primitive state is consecutive and not formative of this battle. If it was actually a battle at Covadonga, i doubt that the Christian said "Let's fight it, in order to change the symbolical identity of this semi-pagan place after our victory, and make it the historiographical foundation of Asturias'.
I don't think it's irrelevant, because "another place" may have been even another place meaningfully different. For example, it could have been a "reconstruction" of the battle fought in the passes from the Meseta to Cantabria and led by the duke of Cantabria (an event that historically is a more incotrovertible fact), and that changes a lot the light of this discussion.
It changes some tactical and features of the POD, yes. But, not that much. After all, this region was quite small (the fortified one around Europe's Mountains) and as you said, these valleys are quite similar. So, strategically the change wouldn't be so great to have great consequences as a POD.
So again, the light is more about details here than what could change if a battle in the central Asturias turn in the Muslim's victory.
You're focusing on the symbolical range of Covadonga before and after the first half of VIII. Nobody denied the high mythification of this battle and the uncertitude about the emplacement, the date or the fact it's a reconstruction or not.
Regarding the valley of Dobra, well the way from Meseta by Ambieva is not shocking and could make sense, as it was used as a way to the other side of Cantabria's Mountains since the Antiquity.
Then, yes, the reconquista legendarium have used the pre-700, pre-christian and even prehistoric features to base itself (The Church of Canguas is a good exemple), but it didn't demonstrate the impossibility or the unlikely of the battle itself.
Since we have not archeological evidence, or other testimony about it, we can't say with any certitude that which emplacement or which not was the one of this battle.
Regarding the memory's reconstruction, maybe it was indeed a reflexion of another battle in these mountains, but the Cantabrian were the theater of many raids, many battles during the VIII-XI era that it could be place for two, three, etc. battles in the same aeras not forcefully connected.
Now, i repeat it, the observation you made are interesting, and because of the too great blur about this, when i re-wrote my TL about this period, i "changed" the place to Ambieva. I just think we're agreeing, but talk about two different faces of this subject.