I have a PowerPoint presentation in which three consecutive slides each
have an org chart. The style and font size is the same in all three
charts in the Org Chart application, but in the slides themselves the
charts are different sizes, depending on the number of boxes in the
chart, and the length of the names in the boxes.

Setting the org charts to 100% of original size in "Format Object"
doesn't make the letters match in size, and I have tried several other
rules, such as setting the object width according to 3cm per box, i.e.
15cm for a five-box-wide chart and 9cm for a three-box-wide chart, none
of which work. The text turns out different sizes in each slide, making
the presentation look very amateur.

How can I make sure the text size presents the same in all three slides?