The original question was about why the payouts might not be the same each quarter, so the issue is the size of the dividends, not how many companies pay. To simplify matters, assume the fund owns an equal dollar amount of each company, each of which pays out 2%, split into four, two, or one as appropriate.
If foreign companies are much less likely than US companies to pay four equal dividends, could that explain why the December dividend is so much larger than the March dividend? Instead of a formula, use 50% pay only in December, 20% pay twice a year, and 30% pay four times a year. Only 30% of the companies are paying in March, and they are only paying 0.5%. That gives me a 0.15% payout in March (and September). What percentage of the total payout for the year is that?
That's easy. The total payout is 2%. 0.15% is 7.5% of that total. What percentage is paid in December? What multiple of the March payout is the December payout?*
* I got 9 times as large.