How to set stylus detection distance on Fujitsu Tablet PC under Debian 10?

I currently use a Dell Latitude 7350. As I'm a teacher, I want to record myself when correcting exercices or tests. I think it's more interesting than a plain typesetted corrected document : I can *say* things I would not write otherwise, and pupils cand more easily perceive the paths one mind should follow in order to answer questions in the most efficient way. But I have two major flaws, with my Dell - whose screen is tactile and supports an active stylus : - the software I use is not palm detection ready (I use Xournal to annotate by hand the PDF documents containing exercices and tests). I bought graphic designer's gloves, but two of them put one over the other are not sufficient to prevent palm detection ; - I cannot record my voice : the embedded microphone records as well hit sounds from the stylus - that are very annoying - and the jack for external headset with microphone is absolutely not handled by any kernel from Ubuntu 16.04 to 18.04. I asked a question for this peculiar problem, with absolutely no success : https://askubuntu.com/questions/1166866/sound-recording-issue-with-at-least-all-ubuntu-version-since-16-04-and-broadwe . I also Recently, I was given a Fujitsu Lifebook T4215 - an old Tablet PC running under Windows XP. It also has a stylus, but the screen is not tactile : it comes with integrated Wacom technology, especially a passive stylus. I installed Debian 10 with LXDE, in order to cope with the old Core Duo T7200 and 2 GB of RAM. Everything is fine, the sytlus is well handled by the system... but I cannot write with it as it is detected as far as 1 cm from the screen ! So writings are completely invaded by parasitic traits : reading them is at least unbearable. I'm going to think I'm cursed. Does anyone has an idea for, say, setting the detection distance for the stylus, or forcing contact with the screen before reacting to any action of the stylus ? Thanks in advance...