Bigger is always better of course but I doubt that a bigger tank would remedy this issue.The fish does not get burned from running into the heater but rather from lying against it as has already been touched on in a previous post.Most keepers go minimal with aquascaping because dats more than likely will hide most of the time if cover is privided.If this has happened twice, maybe he needs a bigger tank/ more swimming room to keep him from running into things. It seems like more Datnoid keepers go minimal to no aqua scaping.
I have very few hideaways for my dats but I avoid bright lighting which seems to keep my dats at ease and moving around the tank.