The phrase "a proportionately small" is correct and usable in written English.
It can be used when describing something that is small in size or amount relative to a larger context or total.
Example: "The budget allocated for marketing was a proportionately small fraction of the overall expenses."
Alternatives: "relatively small" or "comparatively small".
The bully frogs' victim is Hugo, a small frog - with a proportionately small croak.
He is otherwise known for: the buildings he has named after himself; a couple of TV shows he has hosted, the names of which escape me now; his hair, which he recently averred is his own; his vast fortune, about which he can't stop bragging — and a proportionately small mouth for someone famous for having such a big one.
When living and working in a small community, you might think that your business is limited to a proportionately small number of resources.
The movement out of food security into food insecurity from the dry to subsequent rainy season was expected, largely because the major harvest took place just before the dry season, but it is worth noting that for agro-pastoralists, a proportionately small additional number of households became extremely food insecure compared to those who came out of the food secure category.
Helicobacter spp. represent a proportionately small but significant component of the normal intestinal microflora of animal hosts.
If these arguments were removed from the output, average precision for both drug treatment and preventive intervention data combine would increase from 35%to80%0%, with a proportionately small effect on recall.
However, its two lesser-known relatives, the pygmy and dwarf sperm whales, are quite the opposite, having a proportionately smaller spermaceti organ as well as body size.
Besides, the price was more than $1.4 million, which would have meant a proportionately smaller down payment and a larger mortgage — just what they wanted to avoid.
The propulsor is a propeller with a somewhat higher discharge, or jet velocity, than that of the helicopter rotor to match the flight speed, and it has a proportionately smaller area than the latter for a similarly sized aircraft.
From these cases the state court concluded that West Virginia's requirement was constitutionally defective, because the votes of these who favored the issuance of the bonds had a proportionately smaller impact on the outcome of the election than the votes of those who opposed issuance of the bonds.
