If it is the same as the SSI specification, then here is the quote from their spec:
"The heights provided are from the t
op of the baseboard. A baseboard thic
kness of 1.57mm [0.062”] nominal is
highly recommended to ensure baseboard features mate
properly to corresponding chassis features. A
secondary-side clearance of 3.00mm [0.118”] is
available for leads and backside components. "