What aspects of a tube amp/preamp contribute to "holographic" effect on soundstage?

Can someone explain to me is there any part of a tube amp or preamp that contributes to a more holographic image than another otherwise similar tube amp/preamp?

For example, listening to my PrimaLuna Evo 300 integrated - moving between triode and ultra linear mode. I have read that the ultra linear mode is more "solid state" sounding and has more linearity through the frequency range as opposed to the smooth finesse in the mid range of the triode mode.

However to my ears, using KT 150 power tubes in this unit, in the ultra linear mode I seem to hear greater depth of the layering, what I would call "holographic." The cymbals, piano, bass, vocals, etc all seem to occupy a more defined space front to back in the soundstage than in triode mode. Triode mode in this integrated seems to have a flatter presentation across the left to right soundstage - not as deep or into the room as ultra linear.

Perhaps this is unique to PrimaLuna since there is higher distortion (and higher gain) in the ultra linear mode it is presenting as more "holographic." 

When I owned a Luxman MQ88uSE, which I believe used a triode mode with KT88s, I remember there was MORE of a holographic effect - or a "deeper" soundstage than the Evo 300 in either triode or ultra linear mode. So it is hard to square a direct comparison between the two as to what would affect the deeper/more holographic sound of one amp over another.

Is there any known aspect of tube amp topology that can directly be related to being more holographic versus less holographic? Like KT88s will always be more holographic, or triode mode will always be less holographic, etc?

Thanks!