Question: strange arrow behavior

setupdiagramMQ.    

I am having a strange experience with the arrow command.   In the attached worksheet, one can see that plot structures h, i & j and l, m & n are both doing the essentially the same thing:   A vertical line is to be drawn and arrows pointing up and down from the two endpoints are to be added.  The arrows are all of the same length, 5.  The arrow heads for  i & j are what I want but I can't seem to make the arrow heads determined by m & n to look like that.  Whatever values I put in for width of body, width of head and ratio of head length to body length, I get the same wrong output.  

Does anyone have an idea why?

Also, this picture is to be one of many figures for a paper that I am publishing.  What is the best export file type to produce the clearest picture.  The two curvalinear expressions (a parbolic arc and an ellipse) are produced with 10,000 points but still look a bit jagged.  Even 100,000 points doesn't fix this entirely. 

Any ideas?

Thanks.