Same here, HED Belgium and Zipp 303 Firecrest.
I just remeasured the Zipps since they're on the bike now and the tire measured 26.68mm (new tire maybe hasn't stretched out yet) and there's 4+mm on each side and above. Last time the Belgiums were on I measured the tire and it was 28mm on the nose and there was plenty of clearance.
I'd be curious to see how much larger 28s would expand to on these rims...but not enough to try it.
