Refering to my measures, the former one was 4mm. 25 years later it may shrunk, but I guess 6mm is too much (I see you have got 6mm).
I'm simulating the foam since days, and I start to think that 3mm should be enough, I suppose.
I can't assemble the front panel with the cash panel without fixing the later to the rear cabinet first, maybe that way I could see how much gap is it between both panel base and the front panel border but I'm not ready yet for that process. If you can give me more infos it would be great. Thank you!
Also, I wonder about the lenght of your foam. Maybe you didn't put enough (check pic#2)