OMG you are correct. I would have never thought of that. So back in the day when Donzi and possibly other manufactures built the transoms they didn't do the whole transom 2" thick with wood and glass. On my boat the transom where the wood and glass are 2" thick is only between the stringers from the bottom to the top. They also did the same thing where the trim tabs go. The rest of the transom is only 1/2 thick glass at best. I was blown away the first time I saw it. The other crazy thing is the transom is bowed not flat. Maybe that's one reason? I will try and send some pics.

here ya go