I thought only the bottom was tempered for large tanks as well but I'm afraid to take the risk because I got a quote and it was $200 just for a new back panel
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First, $200 is hardly a big expense if you have a 200G tank. Get used to that.
Second, I suggest you take the risk because:
Usually only the bottom will be tempered.
The alternative is a siphon overflow, and the risks of that causing more than $200 in problems is very high.