Ullage is a factor that some are more comfortable with than others & that comfort level is personally subjective. Objectively, wines that are at top shoulder and upper shoulder is normal for a 30-40 year old vintage. With our 50+ year olds, the provenance meets our standards, so please feel at ease when observing the variation.
From Decanter Magazine,
‘It is often the age of the wine that will determine whether ullage is of concern,’ said Sewell. ‘A bottle naturally evaporates very slowly through the permeable cork, so it is only expected that a 40 year old bottle will be less full than a current vintage of the same wine.’
How Christie’s assesses ullage risk:
"'Top shoulder’ is normal for any claret 15 years or older, while ‘mid-shoulder’ isn’t abnormal for a 30 to 40-year-old wine," says Christie’s in guidance published in 2013.
"Ullage refers to the level of wine in the bottle. The older the wine, the lower the level may be. If the ullage is above the bottle’s upper shoulder, there is less risk that the wine has leaked." Christies, 2012.