Why did they pair Red Leader and Red 5? Since that same shot is used first with Red Leader's trench run before it was used again for Luke's trench run, maybe Red 5 is instead standing in for Red 10 or Red 12?
Yes, it is apparent that Muren favored the
Red Five and
Red Leader hero models for filming, even at the expense of accuracy. Why? This was before even Sony Betamax had been invented - most folks didn't watch major motion pictures at home for the most part (except those few short clips sometimes available in 8mm). Most people had to go to the theatre. This business of "pausing" and "screen capturing" didn't really exist yet, so minor details which last only a few frames probably did not concern them too much - just a theory.
Why Red Five and Red Leader? The script never called for them to be together. Well, they do seem to be, after all, arguably the most detailed and nicely finished, and have all of the extra features that the hero models had. Maybe they were also the more "well behaved" (less mechanical problems, etc.) The Red Three always seemed to have more droopy upper wings.
Red Ten and Twelve were pyros (albeit "nice" pyros, or at least Twelve was). But apparently no footage of pyros exists in the final film other than the few seconds when they are exploding. Therefore there is no footage of a Ten or Twelve model flying down the trench (nor Red Four or Six for that matter).
I studied the film again this weekend to verify this. The majority of all X-Wing
model shots in ANH are
(in order by usage) Red Five, Red Leader, Red Two, Red Three. Of course, it's better to study the original theatrical version, not the "Special Editions".
In fact, after Luke's torpedoes hit home, we see
two "Red Leader" hero models heading straight towards us, with the Deathstar in the background. After the station explodes, we see Red Leader (left) and Red Five (right) returning to base.
If you can pause the film just when Red Twelve begins to explode, you can see that it is actually the Red Two hero model spinning around like a feeding alligator! The model was unharmed - the explosion was added as a double-exposure instead of an actual model blowing-up. This method was also used several times in ANH.
The ILM cinematographers were extremely clever, that is why we admire them. The scenes where there are three X-Wings approaching the Deathstar are all Red Five! The engines look more dim and detailed on one of them, but if you look closely, it is the same model. Engine lights were filmed seperately. They could control the exposure, therefore the brightness of the engine glow. All they had to do was change the exposure for one of the engine passes to achieve the different look - brilliant!
They also changed the color of the X-Wing engine glow. Examination of the models shows that the engine lights were white with a red center on both X-Wings and Y-Wings. However, they chose to change the color of the X-Wing engines (perhaps as an added disctiction between the two) from reddish white to more violet-white. This could have been done photographically through the use of color filters or corrective filters for different film stocks.
It was only done in ANH - in ESB and ROTJ both X-Wings and Y-Wings appear to have reddish-white engine glows.
So sorry to ramble on, just so many details! The ILM guys were great!