McPherson strut fixed lower mount

With a fixed lower mount that is not adjustable is the 1/3 droop and 2/3’s bump still applicable if so can you only lower the vehicle to achieve this target and this becomes the ride height

I assume you mean the lower spring mount?

If you are happy with the spring rate, you can use different length, but same rate, springs and/or spacers/helper springs to adjust the ride height within the limits of the strut's travel and/or pre-load limits.

The 1/3 to 2/3 position is a guide, and some applications may skew it one way or the other - especially when variable rate springs, multiple springs, and/or "bump stops" are used.