This may be anecdotal, but I ran into this exact same issue a few weeks ago. The suggested 20% was significantly higher than the 20% on the bill. It took me a little bit to figure out, but we were at the restaurant for a steak special and happy hour. The 20% tip was for the non-special price. For example, the steak and two sides special was $18, but the normal price was $28. The drinks were $5 but the normal price was $8. So the suggested tip was 20% of $36, not 20% of $23. These aren’t the exact numbers, and there were two of us, but you get the idea. The POS/Tip suggestion is setup so the servers don’t get the shit end of the stick when the restaurant is doing a deal/special. I’m not sure I fully agree with it, and I have my own beef with tipping culture in general, but I’m just looking to explain what might be seen in OP’s photo.