Another thing is that if you don't confirm off of a heavy, the most you'll get off DM > Neomax is 750ish. With the full 3 meter HD combos off c.B c.A f.B you can still get over 800 damage in the corner. This is mostly due to loveliness of EX Geneikyaku and how it still does mean damage even when fully scaled. (Numbers might be a bit off, but that's about where I remember from when last I was testing things)
Also, regardless of if the fireball hits, Robert's ranbu will still hit when close enough to the corner. So really, there's no reason not to throw the fireball unless you have trouble canceling it into DM.
Later tested. Off c.B c.A f.B damage for simple HD dp, fireball, dm, neomax is 772, while optimized was 815.
dp, dm, neomax 727
dp+c, fireball, dm, neomax 737
On another note:
4 Meters + HD 950~ Damage Corner
j.D, s.C, f.B, HD, s.C xx dp+C, DC, qcb+BD, qcf+P, dp+C, DC, qcf+C, dp+A, DC, qcb+K, dp+C, DC, qcf+A, fbf+BD, DC, qcfhcb+BD
Leave off the 2nd f.B to give just enough time for Robert to cancel EX Geneikyaku into NeoMAX.