Hello.
1) What they tell you on reddit is correct, the problem is that you are using the same words to refer to 2 different things, with different percentage values.
My answer to your question was "no" precisely because you are misusing the term and that leads to confusion.
the "percentage that you receive for each copy" is the value that steam actually pays you for each sale made, but it is used AFTER a sale (typically around 55%).
You are looking for an estimate of the profits that the game will give, that is, a future value(typically around 33%). That is why they are different percentage values.
Saying this in words can be confusing, so let's look at an example.
Imagine that you estimate that you are going to sell 30 copies. you release your game and effectively sell 30 copies.
You sell 24 in the USA for 20 dollars. = 480
You sell 6 in Russia for 5 dollars = 30
Total sales = 510.
Of those 510, you must discount the VAT and the steam part. You have about 55% left (I say "around" because there are tax withholdings and VAT is variable).
510*55%=280 (The amount you receive from sales)
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Your calculation, start with estimated sales as total price in the USA * total world sales, that is
30 copies * 20 dollars = 600 dollars in sales. (this is your initial value)
You add the "Regional adjustment" to compensate for sales outside the USA.
600-600*15% = 510
Of those 510 you must discount the VAT and Steam, that is
510*55%=280
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In reality, you sold 510 and received 280
280 is 55% of 510. What they told you on Reddit.
In your calculation, your sales projection is 600, you adjust the international price and you arrive at a profit of 280, but
280 is 46% of 600.
Do you notice the difference?
55% (or 57.5% if you are from the USA and only consider sales in the USA) is the percentage of the actual sales value, that is, a value that you only know AFTER selling.
46% is the percentage of a hypothetical estimate of future sales worldwide, based on the fact that you do NOT know the exact distribution of sales.
If you apply discount sales and refund to that 46% and give more importance to international sales, the value will be closer to 30%. Especially since when you're making projections, it's best to be conservative.
2) This depends on you, it is not an obligation to place a discount at launch, but the vast majority of games are usually launched with a 10% to 15% discount at launch.
Whether or not it suits you is something you should discuss with someone who knows about marketing.