Does improved grapple count in determinig the CMB when casting while grappled

I’ve always stayed away from grapple & overrun rules, but, this time, i can’t ignore it.

The rules says that

A grappled character who attempts to cast a spell or use a spell-like ability must make a concentration check (DC 10 + grappler’s CMB + spell level, see Concentration)

so does the feat, special abilities, objects granting bonus on the grapple check count against the DC of concentration?

Does the bonus like flanking count?