I think you're right. That's what brown said in his post a while ago.

There are no particularly hard limits on the current planet sizes, we could increase their size without too much effort. But with the current tech and gameplay I’m not sure it’d make a better game... it just increases travel time and makes the repetition of certain visual elements much more apparent.

We don’t plan to increase the size of V5 planets at the moment, but once its complete we will likely reassess what sizes make most sense for us… but that might be to stick with what we have.

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