The phrase "are often too small" is correct and usable in written English.
It can be used when discussing the size of objects, items, or concepts that are frequently inadequate or insufficient.
Example: "The portions served at the restaurant are often too small for the price."
Alternatives: "tend to be too small" or "frequently are too small".
Unfortunately, sample sizes are often too small to conclude much.
But prepackaged portions are often too small, in the opinion of 25 percent of men and 20 percent of women.
But health budgets in low-income nations are often too small to attract enough of these skilled workers.
As a compact city, Hong Kong's limited greenspaces are often too small, surrounded by incompatible activities, and fail to meet user demands and expectations.
There is a parallel with America, where listed firms tend to be domestically focused, whereas in Europe home markets are often too small to offer growth opportunities.
Even warehouses geared to filling catalog orders are often too small or too reliant on antiquated order-handling methods to process orders in the nanoseconds of Internet time.
Forces between aligned crosslinked microtubules were often too small to distinguish a binding event by eye.
Apart from the fact that most promoters prefer Brussels or Antwerp, this Ghent landmark is often too small for big bands and too big for small bands.
A common rationale for low security at research reactors is that the amount of fuel is often too small to make a bomb.
With microelectrodes of a conventional single barreled design, the tissue tracks were often too small to be followed by light microscopy to the point of deepest penetration, which would correspond to the implantation site of the carbon fiber itself.
The dose of stem cells in one cord blood unit is often too small for successful reconstitution of the hematopoietic system.
