By establishing the engineer's prior time in the United States in L or H status first, since that counts against the ceiling, and then scoping the assignment to fit the balance rather than the other way round.
Scope the assignment to the status, not the wish
Hypothetical example: the company plans a four-year production ramp and later discovers the engineer spent two years in the United States on an earlier project. Collect the admission history, prior approvals and travel records before the plan is fixed, and calculate the remaining balance. Where the balance is short, consider what can be achieved in the available period and who will be trained to continue, which is a better plan than an extension request that cannot be granted.
If the role becomes managing a team, an L-1A analysis carries a seven-year limit, but that requires evidence of managerial duties rather than a new title. Extensions re-examine the same requirements each time, and provisions about recapturing time spent outside the United States should be assessed against the actual travel record.