How to increase the size of the dot produced by OverDot[]

Question

As the title says, I want to find a way to increase the size of the dot produced by OverDot[]. Here is a simple code

f = (x^2*px^2 - px^2*(px^2 - 1)) + (x^2 + px^2)/2 - 2*x^4;
cnt = {0.002, 0.015, 0.0312, 0.05, 0.15, 0.3, 0.45, 0.5612, 0.64, 0.73, 0.778};
xmin = 1.5;
C0 = ContourPlot[f, {x, -xmin, xmin}, {px, -xmin, xmin}, 
Contours -> cnt, ContourStyle -> {Black}, ContourShading -> False, 
FrameLabel -> {"x", OverDot["x"]}, RotateLabel -> False, 
Axes -> False, FrameStyle -> Directive[FontSize -> 22, FontFamily -> "Helvetica"], 
PlotRange -> xmin, ImageSize -> 550]

which gives this output

We see, that even if I used a relative large fonts size (22), the dot above $x$ (OverDot["x"]) at the vertical axes is tiny and hardly visible if I print out this plot. So, my question: is there a way to increase the size of that dot?

Many thanks in advance.

EDIT

Following @Hector suggestions I used Overscript["x", Style["\[FilledSmallCircle]", FontSize -> 12]] which gives

Answer 1

Is this dot large enough for you?

Overscript["x", Style[".", FontSize -> 200]]

Try Esc bu Esc to put a bullet into the upper place holder.

Answer 2

I'd do it a bit different. One of the problems is that DiacriticalPositioning is an option for OverscriptBox but causes a meltdown when used with Overscript (and OverDot).

myOverDot /: MakeBoxes[myOverDot[x_], StandardForm] := 
 OverscriptBox["x", "\[FilledSmallCircle]", 
  DiacriticalPositioning -> True]