Employer failed to provide top-heavy minimum for past years. Plan is a 401(k) plan and employer makes matching contributions on a payroll period basis. In correcting the past failures, we have calculated the contribution amount, but are undecided as to the starting point for the earnings calculation. Does anyone have any thoughts? The regs appear to be silent and I cannot find any IRS guidance on this issue. Thanks.

Have you checked out Rev Proc 2000-16, Appx B, section 3? Section 3.01(2)(B) might work by analogy.