  Early-phase Type Ia supernovae (SNe Ia), especially those with luminosity
enhancement within the first few days of explosions ("early-excess SNe Ia"),
play an irreplaceable role in addressing the long-standing progenitor and
explosion issue of SNe Ia. In this paper, we systematically investigate 11
early-excess SNe Ia from subluminous to luminous subclasses. Eight of them are
selected from 23 SNe Ia with extremely early-phase optical light curves
("golden" early-phase SNe Ia), and three of them are selected from 40 SNe Ia
(including 14 golden samples) with early-phase UV/NUV light curves. We found
that previously discovered early-excess SNe Ia show a clear preference for
specific SN Ia subclasses. In particular, the early-excess feature shown in all
six luminous (91T- and 99aa-like) SNe Ia is in conflict with the viewing angle
dependence predicted by the companion-ejecta interaction scenario. Instead,
such a high early-excess fraction is likely related to the explosion physics of
luminous SNe Ia; i.e. a more efficient detonation happening in the progenitor
of luminous SNe Ia may consequently account for the early-excess feature
powered by the radiation from a $^{56}$Ni-abundant outer layer. The diversity
of early-excess features shown in different SN Ia subclasses suggests multiple
origins of the discovered early-excess SNe Ia, challenging their applicability
as a robust progenitor indicator. Further understanding of the early-excess
diversity relies not only on multiband photometry and prompt-response
spectroscopy of individual early-excess SNe Ia but also on investigations of
the general early-phase light-curve behavior of each SN Ia subclass, which can
be realized through ongoing/forthcoming transient survey projects in the near
future.
