A compensation event is not the contractual route to go.
Rather, under both NEC3 & NEC4, the 1 day a week within the Working Areas is allowed for under the 2nd bullet of People 1 in the Schedule of Cost Components (although the wording is a little different under NEC3 v NEC4).
Consequently, the 4 days should never have been a Defined Cost in the first place and hence, strictly speaking, not a Disallowed Cost..
As Defined Cost is a cumulative increasing figure as the contract progresses, the additional 4 days can be taken out of the Defined Cost figure .
Having said the above, I suggest a bit of common senses : if the planner has clearly been working on the contract and would be making say a 200 mile round trip &/or overnight stays in order to count as a Defined Cost going forward, when he or she can clearly work effectively from HO and home, then I suggest an agreement is reached to avoid this unnecessary cost (for both Parties as it comes out of the pain/gain) & hassle for the individual. I.e. agree what justification the Client is happy with for the Contractor to demonstrate he or she is working on their contract.
Likewise, looking back, fully not allowing the full 4 days a week if the planner has been working on the contract will create quite a bit if bad blood, so I suggest an agreement is reached for historical time.