Basically the arrowhead is dependent on the scaling, and I would like it so that it wasn't the case, for example when `α` is 1

[![normal](https://i.stack.imgur.com/8y4OH.png)](https://i.stack.imgur.com/8y4OH.png)

Then the arrowhead is displayed as it should, but as I slide `α`, then I get these kind of artifacts

[![a big arrow across the whole graphic](https://i.stack.imgur.com/c0Cph.png)](https://i.stack.imgur.com/c0Cph.png)

The code for the manipulate that I am using is

```
Manipulate[
  ParametricPlot3D[
    {x[t], y[t], z[t]} /. 
      {{x -> Function[{t}, a + b t α], 
        y -> Function[{t}, b], 
        z -> Function[{t}, c E^(t α)]}} /. 
        a -> 1 /. 
        b -> 2 /. 
        c -> 10, 
    {t, 0, 25}, 
    PlotRange -> All,
    AxesLabel -> {x, y, z}, 
    AspectRatio -> 1, 
    BoxRatios -> 1,
    PlotStyle -> 
      Directive[{Red, Arrowheads[.000000000004]}]] /. 
    Line[pts_] :> Arrow[Line[pts], {0, -.1}], 
  {α, -10, 10}]

```

How can I fix the arrows so that I don't get the artifacts while manipulating?

In [the other question](https://mathematica.stackexchange.com/questions/180538) it was suggested to use `Small`, `Medium` or `Large`, or maybe use a numeric value to change the arrows size numerically. However, when using `Medium` or `Large`, this is what happens

[![This is what happens when I use medium or size](https://i.stack.imgur.com/wc4E9.png)](https://i.stack.imgur.com/wc4E9.png)

However, it does seem to work fine on certain perspectives and with a negative value of `α`.

[![now it works ok](https://i.stack.imgur.com/CPYbt.png)](https://i.stack.imgur.com/CPYbt.png)

If I change the perspective or rotate the graphic, then it becomes a mess.

So, okay, I already know I can change the size of the arrows numerically, that is good to know, but is there any way to know what is the best size for the arrow, so that the arrow appears the same size with different scalings of the plot? Besides, it seems that when I rotate the cube or change the perspective, the arrowhead dramatically changes the size, why does this happen?