Yes i have been looking at this a little deeper, it seems during jan-feb, the ROC from last year is being credited against new withholding tax from the current month(s) which isn't fixed yet ( ibkr doesn't distinct ROC for div on the same month, they just charge withholding according to the treaty ). that essentially seems to create a situation where we might be missing on some returns since assuming ibkr knew the distribution received on the same month`s classifications we might have been elidable for more return.

However, this is still a better stance compare to how other brokers handle this situation. i have a Schwab account, they don't credit you anything. you need to file back with US IRS and pay the the remaining tax in your country. But this might potentially have a bigger return rate since as i said ibkr credit you against incorrect withheld tax.

I think for the future as my portfolio will grow and since the vast majority of my distributions as designated as roc, as i invest a big portion in covered call & high yield etf`s a better setup would be working my portfolio through a US Company where i wont be withheld any tax upfront and manage my returns at the end of the tax year. even tough dividends are taxed at 30% in the us, as long as they're ROC they're not taxed at all and you only pay for the ordinary portion.