at 3.5 would the loss be more the ~1g?
No way to know, that would depend on how you run the reaction. Additon speed, temp, ect.
The theoretical 100% yeild would bee around 27 grams from 25 grams MDP2P so your yeild is about 85%. That sounds pretty good, I wouldn't worry. Is the 1 extra hour of rxn time that valuable to you?