While that's great, your personal dispositions have nothing to do with receiving the effects of the Sacrament, which are confirmed ex opere operato.

Actually, this is completely false:

While the sacrament is produced ex opere operato, it's effect is received ex opere operantis, according to the disposition of the subject.

So, for example, if a soul is in mortal sin, the grace of the sacrament is not efficacious in that soul (not because the grace was not produced and transmitted by the confection and reception of the sacrament, but because the ill disposition of the subject did not permit that grace to become efficacious).

Like pouring water into an open, or covered, vessel:

The good disposition will efficaciously receive the grace (open vessel), while the ill-disposed soul will have erected an obex gratiae over his soul (covered vessel), such that the grace cannot penetrate it.