If you are awarded say £1500 you are allowed to top it up by 50% (£750) yourself.
They are likely to offer you 3-5 cars-what they deem fit from what you put on the application form. You are however not compelled to choose on of the cars they have listed, unless of course the car you want is on the list.
It is important to tell them your wife “has worked her way through alot of cars” and only the Karoq was suitable and pain free for her to sit in for any journey. You could also tell the grants team you have already test drove any car that you thought fitted your needs but, you found them uncomfortable for your wife apart from the Karoq. Think on prior and be repared to be asked questions but, stick to your guns.
I received what was a basic grant (£1k) this time last year for a SUV. Given AP’s have increased the basic grant now has got to be £1500 or more, so by topping this up by 50% will see you in your chosen car. You may be lucky and get the full amount or a greater amount than I have stated, as it is on an indvidual basis and to some extent what grant manager you have.