How to define parameter values graphically, under constraints?

Perhaps something like this:

n = 6;
posText[x_List] := Text[Round[Norm@#/Total@(Norm /@ x), .01], 1.3 #, 
                        Background -> LightRed] & /@ x;
rot = RotationMatrix[Pi/15];
DynamicModule[{
  pt = pti = {Re@#, Im@#} &@(E^(2 I Pi #/n)) & /@ Range@n,
  r  = Array[1 &, n]},
 Column@{LocatorPane[
    Dynamic[pt],
    Framed@Graphics[
      {(*The Arrows*)
       Black, Arrow[{{0, 0}, 1.2 #}] & /@ pt,

       (*The Criteria Numbers*)
       MapIndexed[{Text[Style[#2[[1]],20], #1],Circle[#1,.1]}&, 1.1 rot.#&/@pti],

       (*The Cyan Polygons*)
       FaceForm[None], EdgeForm[Cyan], Polygon[pt #] & /@ Range[.2, 1, .2],

       (*The Points*)
       Black, Dynamic[Point[r = MapThread[#1 Clip[#1.#2, {0, 1}] &, {pti, pt}]]],

       (*The Text legends*)
       Dynamic[posText@ r],

       (*The Red Polygon*)
       EdgeForm[{Red, Thick}], Dynamic[Polygon@r]},

      ImageSize -> 550, PlotRange ->1.5 {{-1, 1}, {-1, 1}}], 
    Appearance -> None],
   (*The Footer*)
   Dynamic[Grid[{Table[Norm@r[[i]], {i, n}]}/Total@(Norm /@ r), Dividers->All]]}]

Maybe something like this

Manipulate[
 DynamicModule[{mags, pts, bkgrnd, corners},
  corners = N@Table[{Sin[2 Pi i/n], Cos[2 Pi i/n]}, {i, n}];
  mags = N@Table[1/n, {n}];
  pts = mags corners;
  bkgrnd = {{FaceForm[Opacity[0]], EdgeForm[Gray], 
     Polygon[ Table[r corners, {r, .2, 1, .2}]]},
    Table[
     Text[Row[{"Criterion ", i}], 
      1.05 corners[[i]], -corners[[i]]], {i, n}]};

  LocatorPane[
   Dynamic[
    pts, (mags = Norm /@ #; mags = mags/Total[mags]; 
      pts = mags corners) &],
   Dynamic@Graphics[{bkgrnd,
      {FaceForm[], EdgeForm[{Thick, Blue}], Polygon[pts]},
      Table[
       Text[NumberForm[mags[[i]], {4, 2}], 
        pts[[i]], -1.8 corners[[i]]], {i, n}]}, PlotRange -> All],
   Appearance -> Graphics[{PointSize[.02], Point[{0, 0}]}]]],

 {{n, 3}, Range[3, 7]}]

Screenshot: