Needs["SciDraw`"]

Figure[
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     FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 2}];
     FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 3}];
     FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {2, 1}];
     FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {2, 2}];
     FigurePanel[{
       Multipanel[{
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           XShowTickLabels -> True];
          FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 2}];
          },
         Dimensions -> {1, 2},
         XPanelGaps -> .1
         ];
       },
      {2, 3},
      Frame -> False
      ];
     },
    Dimensions -> {2, 3},
    XPanelGaps -> .1,
    YPanelGaps -> .1
    ];
  },
 CanvasSize -> {5, 3.5}
 ]

Figure[
 {Multipanel[
   {
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 1}];
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 2}];
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 3}];
    },
   Dimensions -> {1, 3},
   XPanelGaps -> .1,
   PanelRegion -> Scaled[{{0, 1}, {0.55, 1}}]
   ];
  Multipanel[{
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 1}];
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 2}];
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 3}];
    FigurePanel[{FigGraphics[Plot[x, {x, 0, 1}]]}, {1, 4}];
    },
   Dimensions -> {1, 4},
   XPanelGaps -> {.13, 0.13, 0.07},
   XPanelSizes -> {4/3, 4/3, 1, 0.3},
   PanelRegion -> Scaled[{{0, 1}, {0, 0.45}}]
   ];
  },
 CanvasSize -> {5, 3.5}
 ]