The rules governing Australia’s biggest companies may only reveal “the tip of the iceberg” when it comes to senior executive pay in Australia.

The collective pay packet of the ASX100’s 10 highest paid chief executives was more than 70% larger than the pay declared in their companies’ 2014 financial reports, the Australian Council of Superannuation Investors says.

Shares awarded in previous years under long-term incentive plans, and chief executives exercising rights to shares as performance hurdles are met, are among the factors that took income to a cumulative $171.4m, 72% more than the $99.6m in reported earnings.

Chris Rex, who leads Ramsay Health Care, tops ACSI’s top 10, with his $9.1m reported income leaping to $30.8m when all other share-based considerations are included.

Peter and Steven Lowy of Westfield are in second place, although more than 90% of their $24.4m total was reported in the company’s annual report.

Some chief executive pay had also been overstated by conventional reporting, owing to companies failing to meet performance targets that allow equity awards to vest.

ACSI said the average cash bonus in the ASX100 in 2014 was up more than 10% to $1.35m, and average realised pay of $5.63m was up from $5.01m a year earlier.

ACSI’s chief executive, Louise Davidson, said there was nothing untoward about the way in which earnings are declared but shareholders might welcome another way of judging whether rewards are excessive compared with the return on their investments.

“Statutory reporting is, perhaps, disclosing only the tip of the iceberg in terms of the wealth accruing to senior executives,” Davidson said.

“While the packaging and disclosure of CEO pay has undoubtedly become more disciplined in recent years, thanks to legislation like two strikes and termination pay as well as challenging scrutiny from ACSI and others, company investors and owners cannot afford to lose sight of the quantum of reward being delivered.”

Top 10

1. Chris Rex, Ramsay Health Care, $30.8m v $9.1m

2. Peter and Steven Lowy, Westfield, $24.4m v $22.1m

3. Louis Gries, James Hardie, $20.8m v $12.6m

4, Andrew Bassat, Seek, $17.9m v $4.2m

5. Andrew Mackenzie, BHP, $15.6m v $7.8m

6. Colin Goldschmidt, Sonic Healthcare, $13.4m v $3.8m

7. Gail Kelly, Westpac, $12.9m v $11m

8. Ken MacKenzie, Amcor, $12.7m v $8.4m

9. Mike Wilkins, IAG, $11.5m v $7.5m

10. Nicholas Moore, Macquarie Group, $11.4 m v $13.1m