Judges have delayed their final ruling in a case where lawyers for Wales' ambulance service are challenging a £1.8m compensation award to a family.
The ambulance service did not dispute liability for the fatal crash
Gordon Williams, 49, died in June 2001 when his car collided with an ambulance on the B4350 near Glasbury, Powys.
His widow Jennifer, 59, and three children won the award based on the £4m wealth and earnings potential of the Hay-on-Wye builders' merchant.
A decision at the Appeal Court in London was reserved to a later date.
The compensation was awarded by a judge at Cardiff County Court in June last year after hearing Mr Williams had built up a business and property empire "from zero" through his determination and flair.
The court was told Mr Williams also had an abiding passion for steam engines and had a collection of vintage machines valued at around £500,000.
Mr Williams was pronounced dead at the scene of the 2001 crash. There were no patients on board the ambulance.
The Welsh Ambulance Services NHS Trust did not dispute liability for the incident.
However it has challenged the compensation award to Mrs Williams and her adult children, David, Sarah and Ruth, on the grounds that the trial judge was wrong to find the family so heavily dependent on Mr Williams's earning power.
At the Appeal Court, William Stevenson for the ambulance service, argued the family business was doing "as well" as before Mr Williams's death, so the level of his family's financial losses had been greatly over-estimated.
The court heard David and Sarah Williams had taken over their father's businesses, including the builders' merchants FJ Williams of Hay, and had later made a "spectacular" if unexpected success.
Mr Stevenson said the £1.8m award was effectively a "windfall" for the family.
Lady Justice Smith said such an argument risked ignoring the immense energy and imagination of a man like Gordon Williams.
She added there was no telling what he might have achieved financially over the next 20 years had death not intervened.
She said the "underlying reality" was Mr Williams had "generated a huge amount of money from which his family all benefited" and "there was every reason to suppose he would have carried on doing so".
She said there appeared to be a "reality gap" in Mr Stevenson's case.
Mr Stevenson replied: "Your ladyship has the last word".
Judgement was reserved until a later, unspecified, date.