Am I right in understanding that for contribution to a Roth IRA, filing jointly, both spouses' income will be combined and considered for whether they can contribute. However, for conversion through the backdoor, each spouse's existing traditional + simple IRA will be considered for tax purpose separately? I.e., if tax needs to be paid on the conversion for the wife, it only takes into account whether that her traditional/simple IRA has existing value, not the husband's? thanks.