with the new game next levels sizing being the same as last year the size of the the robot should be the same. My concern is that the rules state 11 by 20 by 15, no problem. But the starting position is bounded by the inner edges of the long black lines, outer edge of the short black line, and the top most outer edge of the field perimeter. So the specs for the field have a tolerance of +/- 1 inch. So if my teams robot fits within the size restrictions but the field tolerance is on the small side, what happens does the robot get to compete or are they oversize? Last year I had a team that passed inspection and every time they came to the field the head ref would size the robot. Extremely discouraging for the team when they did no modifications between matches.
There will be no +/-1" tolerance for size due to field tolerances. If you can measure it with a ruler or the field arrangement it will be fine. The +/-1" tolerance is there to give leeway in placing the field elements.
Also, remember that since the wall is included in the measurement spec (inside side blacks, outside edge short black, and wall) that you can have a robot that is 20" on the floor. It has to be 19" on the floor size with 1" length added that is higher than the wall. Total 20"
+1 to everything above. Also, if possible try and encourage the kids to build the robot a quarter inch within the limit to avoid what you described. I had a sizing box bit once that was 1/4 inch to small in every dimension for this purpose. It makes for as smoother experience for the kids.