Assumption: The value of Interactive Corp doesn't change. And if you look at the stock price, it actually was going down. The true market value of a stock are the number of shared that are publicly traded. The highest traded volume of IACI (in the last 12 month) was 32M shares. With the current market capitalisation of 15B this is about 5% of the outstanding shares.Let us assume, that the percentage of publicly traded shares is about 4 times of that. Why would one want to count the publicly traded shares only? The idea is: the market can't take in any amount of shares, so demand and supply regulate not only price but also volume. If stocks are thrown on the market in large numbers the price would suffer. Therefore the sellable stocks represent the true value. Because even if something has a stellar price tag, if one can't sell it, it's worthless. I would call that "capital in market". In our case the capital in market is about 3B. So the new shares are worth not 1.85B but 370M. Suddenly the deal looks much more reasonable.
I'm sure I've violated any established economic calculation, however I think it's not beyond reason.