maximum 10 number  

This is mainly depending upon which EOR processes is under discussion.

I do not know specifically EOR processes, but I can tell you that the use of proxies is always limited by the knowledge of the issue and the availability of variables, determined or determinable.

In my experience I've read articles that used models where proxies equaled or exceeded the number of variables determined: many of these items have been heavily criticized and, in some cases, removed.

I wish you good job