Legally you are okay to go a dark as you wish from the “B” pillar back !.
Worth remembering that what ever shade you go for, it will be darker looking out when at night or when it has been raining !.
ZS EV Gen1 has pretty much clear glass, where as the Gen2 model has a slight tint to the glass from the factory.
If you go too dark from the “B” pillar back, then the transmission from the rear door to the front door will become very noticeable.
I done to personal choice really.
The guy who tints our cars, has been doing it for over 20 years.
He will not tint from the “B” pillar forward.
But I know Global will !.