VNRecognizeTextRequest does not recognise single letters

I use VNRecognizeTextRequest to recognise a series of letters drawn by hand in the app.

When I draw a few letters, it usually works fine.

is recognised as "LV"

But if I draw a single letter:

or

in most cases, I get zero observation, even using recognitionLevel3.

But this was recognized as "V":

It is apparently not a question of how well drawn letters, as even this was recognised as "LI":

However, this one was not

I have even tried to add custom words, to no avail: request.customWords = ["I", "V", "L"]

General observation is that single letters are rarely or never recognised, dual letters may be recognised ; 3 letters are systematically recognised.

But, I have now increased the brushWidth, and it works much better, even with single letter:

What tuning of VNRecognizeTextRequest do I miss ?

VNRecognizeTextRequest does not recognise single letters
 
 
Q