Change invoice counter to two places

Hey there,

are there any (technical) reasons, why the invoice counter MUST have 4 digits? So far, I created my invoices by this scheme: YYMMXX, like 200804 (the 4th invoice in august 2020). In this way, I can create 99 invoices per month, which is more than enough, since I have just a few per month.
My approach in dolibarr is like this: {yy}{mm}{00@99}. But the GUI forces me to use {yy}{mm}{0000@99} at least, which creates A LOT of zeros (20090001).

I do not get this point. Even from a database perspective, my scheme could be a unique database key.