If the conversion price is fixed at 80c & the sp rises to $1.00...

If the conversion price is fixed at 80c & the sp rises to $1.00 over 3 years the holder of the notes will get a return of 8%×3=$24% interest plus 20% capital return a total of 48% return in 3 years.
That's a pretty big return from a modest share price increase for a company that will be self funded for future growth & strongly profitable/ cash generative.

There is no need for a 'high preference price' as you put it, the potential return on these notes is 100%+ in 3 years if the share price returns to $1.40+ which IMO is very likely.

Assuming the terms are inline with how I speculated I see the Convertibles being 90%+ taken up especially if they allow holders to buy more than their entitlements.
I personally would buy a lot more than my entitlement.