FancyBear,
I'd go at it a different way - find out how much an engineer with the same number of years all with the company would get, and compare your offer to that - if it's less, argue that you're worth the extra days because of the experience you offer.
That might or might not work - it didn't initially work for me when I signed on at my present employer - but I did manage to get it later (under a different boss) - there was a wage freeze that year
but my boss during the annual review indicated that he was pleased with my work, so I hit him up for the difference in vacation - it passed, as that meant no more money directly out of corporation pockets.
Still, also look at comparable corporations, and if your potential employer is significantly lower (even if they offer you what would be normal for them), try to get more vacation or compensation based on the idea that you're giving up these things to work for them...
Good luck!