I recently took a couple of ill-advised fights against a large bounty target. I managed to walk into a few torpedoes and lost most of my fleet. However the proportion of crew I lost did not appear to be in line with the capacity of the ships I was working with.
I started the battle with a fleet of an Eagle, a Falcon, a Wolf and one Tug. I deployed the Eagle and Falcon, losing them both and subsequently announcing a retreat. I successfully disengaged with the enemy only to find my burn speed reduced to 0 (although I could still move slowly) as what appeared to be a bizarre clowns-in-car scenario arose where I had over a hundred and fifty crewmembers packed into one Wolf and a Tug.
The fleet I had just lost to then repeatedly ran me down and harassed me but wouldn't force an engagement as it thought I could escape. After a couple of minutes of repeatedly clicking through harassment dialogue my logistics of 0 eventually destroyed my last ships and I escaped the cycle, though not before the Wolf was destroyed by a critical accident leaving 99 crew (significantly more than half) still standing around on my tug alone.
I'm not sure how crew is really handled, but I would guess that when my cruisers were destroyed I lost crew close to their normal operating capacity, rather than some amount proportional to how many people I could support with my fleet. To be clear I wasn't significantly overcrewed (or at all iirc) when entering the fight either.