Normally you woud put everything except the drawing border in model space and view it through a viewport sized to fit the border.
(But every company has their own way of doing things).
I'm not sure just what issue you are having, is it that the arrow heads are too small?
You could either draw the arrows directly on the Xrefs in Model Space and set dimension scaling for the arrows so that the heads show large enough in PS.
eg. If you have the viewport scale set to 1:10 then you would set the dimension scale for the arrows to 10.
Alternatively you could set the actual arrow size to 10x what it is as standard and leave the dimension scale at 1.
Or once you have the viewport scale set then you could close the viewport and draw the arrow in PS at scale 1.
The problem with that is that if you rescale or pan in the viewport, or if you move the xref in MS, then the PS arrow won't go with it.
Hopefully that has given you a few ideas, if I've misunderstood your question or what the issue is then please come back.
Im intelligent enough to know that I dont know everything; but I'll tell you all about it anyway.