How can I make the vectors (vector heads) larger in a StreamPlot?

Question

In my StreamPlots, the vectors can hardly be seen, in particular, since the heads of the vectors are so small.

Can I change this?

Example:

StreamPlot[
Projection[{x (-x + f), y (x - y + f)}, {-y, x}], {x,-1,1}, {y,-1,1},
StreamPoints -> {CirclePoints[20]}]

When I use this image in a document where the size of the image is much smaller, one can hardly see the vectors. Is there a way to make the vectors more visible even if the image is small?

Answer 1

StreamScale will affect the size of the arrowheads:

StreamPlot[
    Projection[{x (-x + 1), y (x - y + 1)}, {-y, x}\], 
    {x, -1, 1}, {y, -1, 1}, 
    StreamPoints -> {CirclePoints[20]}, StreamScale -> Large]

or

StreamPlot[
    Projection[{x (-x + 1), y (x - y + 1)}, {-y, x}], 
    {x, -1, 1}, {y, -1, 1}, 
    StreamPoints -> {CirclePoints[20]}, 
    StreamScale -> {Automatic, Automatic, 0.025, Automatic}]