Unsteady flame propagation within a narrow channel, namely a Hele-Shaw burner, exhibits complicated phenomena. Recently, a new narrow-gap-disk-burner (NGDB) was developed, of which the disk-gap could be varied continuously and precisely. Although various complicated flame structures have been observed successfully, their dependency on the initial ignition has not been clarified. In this study, the volume of the ignition part was varied to introduce disturbance at the ignition stage, and the propagation characteristics of premixed methane and propane flames were investigated. Conclusively, quenching distance was not significantly affected by the ignition volume, especially in propane-rich conditions. In contrast, the flame structure and propagation velocity were sensitive to the ignition volume if it was larger than a critical volume, and when the disk-gap was approximately 1.5 times the quenching distance. A strong initial disturbance could generate complicated cellular structures coupled not only with shear stress but also with heat transfer. These cellular structures could increase the flame propagation velocity when the Lewis number was sufficiently smaller than unity. In contrast, the flame shape became smoother when the disk-gap was sufficiently larger than the quenching distance. Thus, the flame propagation velocity was comparable to the laminar burning velocity when it was less affected by the initial disturbance.