I think I have this [ solved ]. These methods works for me anyway.
In Gravit Design you can make polygons in many ways but if you want them to line up you have to create them in particular ways.
First Method: I’m going for a side of 100 px. Click Shape > Polygon. Left click on the middle point and drag UPWARD vertically until you get about the right size and release. On the right panel change “points” to 5 and you have a pentagon with the bottom edge horizontal. Click Shape > Polygon again. Left click somewhere below your first shape and drag to the RIGHT horizontally to make the hexagon and release when the size is about correct.
To adjust the sizes so the SIDES of both shapes to 100 px: With the pentagon selected, change the Size “W” (width) to 161.8. Select the hexagon and change the Size “W” (width) to 200. Use arrow keys (or shift-arrow) to position the hexagon below the pentagon.
Note: From the wiki page, the pentagon width is 1.618 times the side value.
Other methods are to start the pentagon with either a triangle drawing from middle upward and changing the point value to 5 or a STAR drawing from the middle upward again and changing to SIZE to 81% to make a pentagon.
Works for me