Pathfinder Companion Subscriber
Normally, an Eidolon gets an ability increase every 4 HD it has. Does a synthesist summoner gain an ability increase once every 4 HD of his Eidolon as well, on top of his own ability increases?
The Synthesist uses the Eidolon's physical ability scores when fused with his Eidolon. So if you've increased the Eidolon's physical abilities (and the Summoners Mental ones) You would appear to get both increases, yes.