There is a known concentration of CS units based in various segments of Pennsylvania, Maryland, and West Virginia... also even some up in New York.....

Other causes for more than average to have been created in recent years is for a variety of reasons... The economy has been a major factor... Resident Southern units traveling as much to distant events and programs up in Northern areas has significantly dropped off.... hence in order to have any reasonable force ratio for an event.... Fewer Rebs to be had.... Many resident Federal forces have started to galvanize as Rebs... to help balance the numbers...

More acutely in southern regions whereas the numbers of programs and events tend to be much higher... same token in reverse... fewer Federal troops available. Native Northern based units instead of scheduling and traveling to a dozen or so events a year down South... have inheritably cut back to just a few.... Lots of Rebs... few Yanks... in response more and more native CS units have started to galvanize as Federals for the same reasons... Many of the more reputable units have established a dual role portrayal at their conception... They do both Blue or Grey equally by design.. rather than just the occasional need... So not uncommon these days to find CS units based in New York.... or Federal units based in Va or NC...

There will always be the neo-confederates that refuse to portray anything else... a few on the Federal side likewise.. but most of the more serious historians and reenactors have no problem doing either role as a collective effort of portraying history...
Just an opinion and observation
Frederick