As long as you can create new rectangles and do not need to scale existing ones, a solution comes (currently) to my mind:
1. clone your first rectangle
for example:
Shift: per column x 20%, y 0%
Scale: per column x 20%, y 20%
If you want a size increase of 20% for each uncheck cumulate
If you want a size increase 20% of the previous check cumulate
Rows, Column 1 x 4 (or in your case 1 x 50)
Create.
2. Delete the first clone which is identical to the original rectangle.
3. use the Align&Distribute Dialog
3a) to remove overlaps
3b) to align the tops of the rectangles
You might have to move all rectangles as a whole because "remove overlaps" probably shifts all of them. If you want to color them differently you need to unlink the clones (Shift+Alt+D)

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