Sayyid Sistani's new ruling shows that one only has to pay khums when his cumulative year on year income matches the amount left in his loan account. Supposing someone has multiple loan accounts, is this ruling refering to the total when all the values of the loan accounts are combined? Or simply when the smallest loan account value is reached by cumulative income?

It’s total loan
But ofcourse depending on some conditions which are stipulated in this document

https://www.world-federation.org/sites/default/files/Khums_Guide.pdf

Sayyid Sistani's new ruling shows that one only has to pay khums when his cumulative year on year income matches the amount left in his loan account. Supposing someone has multiple loan accounts, is this ruling refering to the total when all the values of the loan accounts are combined? Or simply when the smallest loan account value is reached?

Exempted loans from khoms are loans that are taken to buy something you still use, such as a loan to buy the house you live in, or the car you use.
In such cases, if the amount of the remaining loan at the end of the year is greater than your profits or equal to it, you do not need to pay the fifth of the profit.