For me, the merit of partial scholarships (except for costing less for the WMF and thus enabling more people to participate) is that the extra money one has to pay form their own pocket serves as a sign of seriousness and commitment on their part.
If the partial scholarships could somehow be defined, for example, to be 75% of the average flight cost from one's home to the conference, then those extra 25% (which could be USD 50 or USD 500....) will show one's seriousness.
Maybe this is a better and fairer way to calculate the partial scholarships than the EUR 300 sum we had this year.
Harel