The phrase "a hefty proportion of" is correct and usable in written English.
It can be used when discussing a significant or large part of a whole, often in contexts related to statistics, research, or general observations.
Example: "A hefty proportion of the participants reported feeling satisfied with the new policy changes."
Alternatives: "a large percentage of" or "a significant amount of".
The generation before us bought up a hefty proportion of British property and are now either sitting on it or leasing it to us for astronomical monthly fees.
The GIB has huge potential to leverage in a hefty proportion of the private sector investment needed for the UK's low carbon economy to flourish.
The real purpose of quantitative easing is to bring down long-term interest rates, which affect the cost of a hefty proportion of American mortgages.
As if Carmina Burana has met High School Musical, the work has been almost impossibly sanitised – the equivalent of pulling a hefty proportion of its teeth.
If you're very worried about Brexit, you might want to take a look at your portfolio for a handful of stocks that have British subsidiaries that generate a hefty proportion of the parent company's revenue.
The study suggests that a hefty proportion of clients are going hungry for longer than the nine-to-15 days that three Trussell food parcels would be expected to last.
And, given the alarming rise in obesity, telling fat people to eat less will alienate a hefty proportion - forgive the expression - of the electorate.
Transposon derived sequences account for at least 45% of the human genome, a hefty proportion when compared with the 1% given over to protein coding regions (Jordon et al. 2003).
Finally, she needs a hefty get-out-of-jail bribe.
American issuers like Ford Motor Company and Philip Morris have brought large new issues to the European market recently, and a large proportion of this years hefty new-issuance calendar in Europe reflects European demand for American names in the single-A universe.
