Arguing with the GAs in this situation is pointless and often counter-productive. I've been in similar situations, particularly flying the older/SkyWest CR9s. I have carry-on luggage that I know fits in every overhead bin in DL's fleet, precisely because I end up on a lot of regionals out of IND. GAs will insist that my luggage will not fit in the overhead bin. Even though I know that it will, I just don't argue. I let the GA scan it and give me the pink tag. Then I just carry it onboard and put it in the overhead bin.