PBGC coverage after divorce

Hello,

Plan originally covered 100% owner and spouse, exempt from PBGC coverage. They have since divorced but spouse has remained as an employee. No Minor children between them. Ex does not have options to stock under 1563(e).

Does the 5 year look back for ownership purposes for PBGC coverage extend to owners by attribution during the last 5 years or is it only if they had 10% direct ownership on their own?