Yes. I don't use software like that myself, but it's easy to overthink this. It's just a matter of simple proportion. So the base malt quantity is 5206 x 12 /38.5 = 1623 g. Which is what you have. And so on.
What I would say is that the original recipe states that it assumes an efficiency of 82%. That is pretty high, and you need to think whether you can achieve that. Then it would be a case of maybe upping the base malt quantity a bit, or accepting weaker beer.
If I was making a 12 litre batch of beer, I reckon I'd be using more than 1600 g of base malt. But that's me, with my set-up.