[Roverlike]

I have yet to find sign where large triangle is at bottom and small triangle is at top. As far as I can find you either have both triangles with same height or the above one is bigger or there is only above one without bottom one.
From my understanding above one is there to signify that you have height restrictions and danger comes from above if you are over the size limit. Bottom triangle is there (if pictured) mere to graphicaly inform you that it is the height size that you need to watch out.
In case of round sign both triangles are usualy the same size, and in triangular sign different sizes are used to attrack drivers attention tomimportant information.

I am interested to find out if there is different answer to this question.