Creating BIP39 passphrase using 3 Polyhedral Dices

Hi, I have come across a very elegant way to map a regular dice roll with the BIP-39 list of 2048 words on Github: https://github.com/veebch/Bip39-Dice

However, this methods requires 11 mutilplications and addition of powers of 2 which of course anyone can add on a spreadsheet and get the result immediately and I woundered if it was possible to get to the same result with only sums (in this case only 4) which could be done with a pen and paper easily.

To do that I use polyhedral dices which you can buy any sets for $10 on any online retailer.

The most commum polyhedral dice you all use is D6 (6 faces) but you have D3,D4,D5,D6,D7,D%,D8,D10,D12,D16,D20,D24,D30,D60 and D100. Yes D100! 100 faces with numbers ranging from 1 to 100.

So with 4 rolls of one D100, one D30 and two D20 dices and four additions we can map the BIP-39 list of 2048 words.

1. We take the BIP-39 word list and map it from 0 to 2047 (2048 words).
2. We use D20 dice to obtain the first 1900 numbers as follows: we do a roll and substract 1 which gives us a number between 0 and 19. So for instance we get a 15, we will then use 14. This first roll will give us the mapping of (19xx i.e. the first 1900 numbers). So we will have a range the thousands (1 and 2) and the hundreds (1 to 9) and 0 for the units.
3. We then use the D100 dice and substract 1 which give us another 99 numbers. Now if we add the previous (thousands, hundreds section) to this dice roll which fibes the units we would now get a range of attainable numbers ranging from 0 to (1900 + 99)=1999.
4. Let's now do a roll a the D30 dice and again substract 1 and we would get 0 to 29 value. This now give us a range of attainable numbers of 0 to (1900+99+29)=2028 words in our BIPS-39 list.
5. Finally, we roll again the D20 dice and substract 1, we would get values ranging from 0 to 19, so we would now get attainbale numbers ranging for 0 to (1900+99+29+19)=2047.

So with 3 polyhedral dices D100, D30 and D20 and 4 sums we can get a range of numbers ranging from 0 to 2047 which we map to our 2048 BIP-39 world list.

Could anyone check and if there's a flaw in construction or if we get so bias of probablities using this method?

Thanks.

https://preview.redd.it/ira4b9mc4dmd1.png?width=686&format=png&auto=webp&s=8ad3cefaabf8b80e3f1cc1be16b473d5498b15f9