Factory will only copy the shape /area of the template -supplied, therefore you need to build-in whatever shape /area of coverage you require.
If your front hairline is actually thinning, as you say, well then, incorporate an inch or so of a ` bridge` between your two temple bits.
Be aware that such a system can be ` fiddly` to work-with...... so your template will look like 2 triangles joined by a thinner / curved strip of material.....what I suggest you do, to make it easier to fabricate, is, slick your hair back /down onto the crown, with water.
Then, proceed as if you were making a normal [full-sized] topper template. Another forum-contributor posted this link recently, so in case you`ve not seen it, here it is again. https://www.youtube.com/watch?v=KFQX0Bv_8N8
You can trim out the required shape from that ....use an eyebrow pencil to mark your skin , at the temples and front hairline, where your hair used to be ....then apply your layers of film and sellotape,,,after the first layer or two, and before you lose ` sight` of the marks, use an indelible marker on the film, to trace the underlying-lines...continue adding your sticky tape [sellotape] to make a sturdy ` shell` .....remove the lot, and just trim out the required -area, with a scissors.
Making a template can be a bit of a ` chore` ...don`t expect to be fully satisfied at your first attempt...you may have to re-attempt it , possibly a few times before you`re happy.... you can post a photo or two here, when you have it done, if you want some in-put into how it looks.
Coloring system-hair is tricky at the best of times....the hair takes color more rapidly and deeply than growing-hair.. it`s best to avoid it in the early stages of wearing as it`s not as simple [usually] as it sounds......lighter shades are the trickiest..... colorists spend a lot of time learning their craft....it`s easy to go totally wrong when attempting to color system -hair. Hope that helps.