Even with an instant trade the maximum exposure freetrade would have is 1 share.
Let’s say freetrade own 0.99 as above.
Someone places an instant order of 5.5 shares.
Freetrade purchase 5 shares and then convert the 0.99 into two 0.5 and 0.49.
The customer becomes the proud owner of 5.5 shares and Freetrade retain the 0.49 exposure.
But let’s say now another instant trade gets made shortly after for 0.5 shares.
Freetrade will have to buy a whole share via instant trade. So the total is 1.49.
The customer gets 0.5 And Freetrade are back at 0.99 exposure.
Obviously end of day trades are somewhat easier - 10 customers all wanting fractionals of the same stock; will all be bough at the same time in bulk. And the remainder of the fraction is Freetrades exposure.