I wouldn’t be surprised at this either. My DD5 is 39.5 in but with tennis shoes on she easily cleared the minimum at any of the Disney charts. Sometimes they didn’t even ask to measure her.
I don’t know about the other parks, but AK is consistent with what we had measured at home and the Dr. My son was 43.5 when we went, 1/2 inch too short for FOP. And he wasn’t able to ride.
I think height is only one part of it. Does he like rides normally? Does he like the dark? Any favourite characters or movies? My son turned four this week. He LOVES rides and is 40" now so we planned to do all Epcot rides, except Mission Space (worried about him getting sick and it is our first park day so I don’t want him to hate rides for the rest of the trip). But we also put in time for meeting characters (so many in world showcase and Mickey and the gang). If we have time we are going to do Agent P’s. Also time for a treat
We did a FPP for TT because it goes down more than the other two and it seems FEA and Soarin have lower wait times lately. Soarin seems to have good same-day FP availability so I’m hoping to get an extra FPP for it later in the afternoon.