I always indicate out to straddle two lanes about 50 yards or so out from the roundabout if it looks too tight. At the end of the day you can’t be penalised for using the amount of road you think is necessary to safely make the manoeuvre, and if it happens that you think you probably could have made it when going round then no big deal. As you say it’s only added seconds on to the person who’s behind yous day and there car potentially stays on the road to live another day.
If had people go as far as driving along the pavement to get past me on some occasions. The only negative outcome would be if said prick decided to still squeeze past you and then inevitably get himself clipped. But then that’s his problem (especially if your fitted with those annoying cameras) as you’ve made your intention clear.
Better safe than sorry I say