Gurps nailed it, you need a different setup. Scroll down the page and look for shop by rough-in.Yeah. The tank is right up against the wall. The newer toilets are about an inch deeper towards the wall, won't fit. Found out the hard way.
https://www.us.kohler.com/us/toilets/article/CNT125900002.htm
Scroll down to step 4
https://www.americanstandard-us.com/parts-support/how-to/choosing-a-toilet
None of these are $39 dollar specials......and not sure if Lowes or home dumps can even order. Somerville or Northeastern?