from my electronics teacher said in the 70's, and still true today.
"humans are stray capacitance to ground", so we are not an inductor, unless you are a robot.
you will also influence signals, the body absorbs signals, so you going near the radio is making the antenna slightly directive.
and everything you have mentioned sounds like simulcast reception problems and solutions.
to fix my simulcast problem we put the radio in the window, and stuck it in the edge of the window, in a cell phone holder turned horizontal.
so you might try the one thing of going near a tower, or trying a yagi, or doing the rabbit ear antenna dance of the old TV days to try and find the sweet spot. and you could buy an SDS type scanner, it is expensive but even i figure it is my future.