Never, ever trust anyone else's measurements for sizes of 40K universe things (or pretty much anything else). 95% of people have no clue as to the actual sizes of things and will generally be happy to give you wildly bad info.
well yes, thats kinda the point I'm making. but I was talking to the actual designers. not just anyone and I expected them to know. had I known you had some to hand I'd've come to you first.
as for the TRUE scale of things. back in 2001 tim adcock was quoted to say that the fury interceptors are;
"...more the size of jumbo jets..." bfg was never supposed to have direct scale references to the 40k universe in it. the scale was always considered slightly mysterious. its only when fw got involved that they decided to make fighta-bombas and thunderhawks and must have had it in their heads that fury's and swiftdeaths were supposed to be one-man snub-fighters. which is (technically)wrong, if you base the original bfg release info as true canon.
furys are clearly very large vessels with multiple lascannon arrays and a modeststly sized crew. (just look in your bfg rulebooks, its all there)
however bfg is (and has always been) a mismatch of scales from the off. the planets and celestial phenomena are not to scale with the ships but to the ships stands. thats why all the measurements come from the stand. the tip of the stand is where the ship actually would be, the circle of the base is meant to represent the aura of the ship's voidshields. so thats where the blast markers go...
I think with fighter/bombers its a case of as long as the ordnance matches the scale of each-other per faction, its fine. so players using thunderhawks are usually only using thunderhawks as astartes vessels are (originally) the only ones capable of launching them. and exclusively them.
however that goes up the wall straight away as chaos vessels can also use them, potentially having swiftdeaths and doomfires in the same fleet as traitor thunderhawks... its a visual mess by the time you get to armarda's release anyway and a lot of the lore and "scale" is simply overlooked for what is cool...
once fw got into the mix it just went even crazier.
so to summerise;
gw originally said that a th would be so small you'd not see it on the tabletop.
fw decided that a th was bigger than a fury (or that furies are one man fighters) and modeled them accordingly
so the final answer to all this?
well the eagle dropship is staying so, I'd say, continue to use the eagle dropship as the thunderhawk size and model your bombers to be just a bit smaller and your fighters smaller still to represent one-man-fighters.
simple...