Circular polarizer with filter holder system

Has it been proven one way or another as to what is the best location for a circular polarizer when being used with a filter holder system?
I've read where some say it's best if the cp is placed farthest from the lens, while some say putting the cp in the filter slot closest to the lens, works just as well.

Lee and Cokin are 2 of the popular filter holder system but yet, they treat the cp location completely opposite.

Is that an indication that the cp location does make a difference or is it just a case of competitors wanting to be different from one another?

I hope it's the latter because, I have a Cokin Z Pro filter holder and now i'm wondering if that was a mistake as I planned on getting a cp for it.

I am interested in answers to your questions as well. Help!

out of curiosity but how would you put a circular polarizer filter in front of a filter holder?
considering that you have to rotate the cp filter to get the desired effect, and at the same time you would have to rotate the filter holder to get your ND filter at the desired angle.

for me, I've always mounted the CP filter first on the lens, filter holder afterwards

It's possibly just down to the filter holder design, but could be to avoid un-polarised light leaking in between any gap that might exist between filter & lens which could reduce the polarisation in your shots. A screw-in filter will avoid this, but your filter holder might rotate with the polariser which would make the use of a ND grad awkward as the horizon would be tilted on the ND grad filter.

taemo wrote in post #16332551
out of curiosity but how would you put a circular polarizer filter in front of a filter holder?

If I understand the Lee filter holder system correctly, there is an mounting ring (105) that can be put on the end of the filter holder.
That allows a Lee screw in circular polariser to be attached to that mounting ring.
Then the cp itself can be rotated independently.

With the Cokin Z Pro filter holder, the first filter slot closest to the lens can be used for a circular polarizer.
I know that Singh-Ray makes a "sprocket" cp that can be used in the first filter slot.
It can be rotated independently as well.

So, with the Cokin Z Pro holder, the cp would be located closest to the lens and with the Lee holder, the cp would be farthest from the lens.

There was a bit of a debate about cp location in the nature&landscape sub forum, Post Your Graduated Neutral Density Sample Shots Please.
Starts towards the bottom of page 3 and carries over for a couple of more pages.
The postings are old and the debate just sort of faded away from what I could see.