A couple Questions-Ramp Checks and Experimental Operations

I sold my experimental airplane sometime ago but I'm looking at buying
another one at this time. I always flew over cities and used my RV-6
just like I would any other airplane with a normal category
airworthiness certificate. But, I remember reading something here
once about some letter that we need from the Feds in order to fly over
populated areas in EXPERIMENTAL category aircraft. What do you folks
know about that requirement?

Also, I really enjoyed the conversation concerning ramp checks on
private aircraft. Just the other day in Sitka Alaska some fed
demanded to ramp check a private airplane operating under part 91.
The owner was scared and confused and allowed the Fed inside of his
airplane. What do you people think of that? I guess the Fed even
told the owner he was going to detain him if he didn't submit to the
ramp check. Interesting eh? Since when was a government puke from
the FAA able to legally hold an airplane back from a flight. Too
much.

How many others of you have had this happen while operating under part
91? Anyone?

Bill