Top heavy determination in a MEP - don't run away!

[AlbanyConsultant]

I have a plan that was sponsored by Company A. Company B split off from Co. A and the plan was admended to make it a MEP so that Co. B could still be part of it (the 100% owner of Co. B is an still employee of Co. A and draws all her pay from there - she doesn't get paid by the company she owns! - so it's not a CG). The employees of Co. B also still work at Co. A, so they are still getting paid and deferring from both 'sides'.

I get that, because each company is tested separately, I'll have to manually break out the deferrals by company for testing (the platform they are on doesn't seem to do sub-accounting), but I'm not sure how to treat them for top heavy. Where do Co. B's employees' balances count for top heavy determination? Should the balance they've accrued up until the division stay in the Co. A testing, and then as part of my split going forward I'll have to track their balances as two sub-accounts for testing purposes?

Thanks for your help.