Well tbf Ichigo has senses someone that attack him from behind (Byakuya, Shinji and probably more). And every spiritual beings barring Ichigo can hide their reiatsu. And he actually has feats of sensing someone from a separate space called dangai.
And even fodder Hollow can do something
like this and Ichigo can react just fine and that's him without shunpo.
And shunpo can do
this.
>Her shadow restraint can't be noticed by someone with city wide sensing good enough to let them sense witches
Well, Beings with higher than average levels of reiryoku possess the ability to sense other spiritual beings without relying on
their five basic senses. But ehh I digress.
Which is why I vote for inconclusive.
Both have way to avoid each other's attack. Ichigo's flight and shunpo is a good way to avoid the shadow stuff and so does Riz's shadow hiding stuff.
Both can technically one shot, Riz with her shadow and Ichigo with almost any attack.
If they decide to do close combat then both of them can use still use their ability (Ichigo used point blank getsuga tensho twice against priveron espada in shikai and I believe she also can spam her shadow in close range right?) this is become a scenario of "who hits first" where both combatant has way to avoid each other's best attack and will likely to spam their best move.
If Riz can caught Ichigo's off guard then I also can argue Ichigo can caught her off guard, he can use shunpo to appear behind her and use point blank getsuga because he do that in character and
Getsuga has pretty good AOE. And I believe her shadow has good AOE too right?
- Conclusion: They both can win, this can go either way.