It takes me 2 engies at lv 116 to OH cap yamato now, and with only my 180 vet
engie, I can OH to 38. (Engies at...170, 170, 174, 180)
2x 170 vet engies...
1x 180 vet engie...
in contrast with my at level yamato... (pre BB43AA)
On topic, yamato's xp is more earned then shared, so more attack, more xp. Also, if
you rely on shared XP, the smaller a room is, the more you'll get.